1 | <HTML>
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2 | <!-- The API of this class and the documentation -- but not the
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3 | implementation! -- are based on that for SGI's hash_map class:
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4 | -->
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5 | <!--
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6 | -- Copyright (c) 1996-1999
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7 | -- Silicon Graphics Computer Systems, Inc.
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8 | --
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9 | -- Permission to use, copy, modify, distribute and sell this software
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10 | -- and its documentation for any purpose is hereby granted without fee,
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11 | -- provided that the above copyright notice appears in all copies and
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12 | -- that both that copyright notice and this permission notice appear
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13 | -- in supporting documentation. Silicon Graphics makes no
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14 | -- representations about the suitability of this software for any
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15 | -- purpose. It is provided "as is" without express or implied warranty.
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16 | --
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17 | -- Copyright (c) 1994
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18 | -- Hewlett-Packard Company
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19 | --
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20 | -- Permission to use, copy, modify, distribute and sell this software
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21 | -- and its documentation for any purpose is hereby granted without fee,
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22 | -- provided that the above copyright notice appears in all copies and
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23 | -- that both that copyright notice and this permission notice appear
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24 | -- in supporting documentation. Hewlett-Packard Company makes no
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25 | -- representations about the suitability of this software for any
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26 | -- purpose. It is provided "as is" without express or implied warranty.
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27 | --
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28 | -->
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29 |
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30 | <HEAD>
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31 | <Title>dense_hash_map<Key, Data, HashFcn, EqualKey, Alloc></Title>
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32 | </HEAD>
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33 |
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34 | <BODY>
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35 |
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36 | <p><i>[Note: this document is formatted similarly to the SGI STL
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37 | implementation documentation pages, and refers to concepts and classes
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38 | defined there. However, neither this document nor the code it
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39 | describes is associated with SGI, nor is it necessary to have SGI's
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40 | STL implementation installed in order to use this class.]</i></p>
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41 |
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42 |
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43 | <H1>dense_hash_map<Key, Data, HashFcn, EqualKey, Alloc></H1>
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44 |
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45 | <p><tt>dense_hash_map</tt> is a <A
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46 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
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47 | Associative Container</A> that associates objects of type <tt>Key</tt>
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48 | with objects of type <tt>Data</tt>. <tt>dense_hash_map</tt> is a <A
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49 | href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair
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50 | Associative Container</A>, meaning that its value type is <tt><A
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51 | href="pair.html">pair</A><const Key, Data></tt>. It is also a
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52 | <A
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53 | href="http://www.sgi.com/tech/stl/UniqueAssociativeContainer.html">Unique
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54 | Associative Container</A>, meaning that no two elements have keys that
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55 | compare equal using <tt>EqualKey</tt>.</p>
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56 |
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57 | <p>Looking up an element in a <tt>dense_hash_map</tt> by its key is
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58 | efficient, so <tt>dense_hash_map</tt> is useful for "dictionaries"
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59 | where the order of elements is irrelevant. If it is important for the
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60 | elements to be in a particular order, however, then <tt><A
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61 | href="http://www.sgi.com/tech/stl/Map.html">map</A></tt> is more appropriate.</p>
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62 |
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63 | <p><tt>dense_hash_map</tt> is distinguished from other hash-map
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64 | implementations by its speed and by the ability to save
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65 | and restore contents to disk. On the other hand, this hash-map
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66 | implementation can use significantly more space than other hash-map
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67 | implementations, and it also has requirements -- for instance, for a
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68 | distinguished "empty key" -- that may not be easy for all
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69 | applications to satisfy.</p>
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70 |
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71 | <p>This class is appropriate for applications that need speedy access
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72 | to relatively small "dictionaries" stored in memory, and for
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73 | applications that need these dictionaries to be persistent. <A
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74 | HREF="#io">[implementation note]</A>)</p>
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75 |
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76 |
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77 | <h3>Example</h3>
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78 |
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79 | <pre>
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80 | #include <google/dense_hash_map>
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81 |
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82 | using std::dense_hash_map; // namespace where class lives by default
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83 |
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84 | struct eqstr
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85 | {
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86 | bool operator()(const char* s1, const char* s2) const
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87 | {
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88 | return strcmp(s1, s2) == 0;
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89 | }
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90 | };
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91 |
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92 | int main()
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93 | {
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94 | dense_hash_map<const char*, int, hash<const char*>, eqstr> months;
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95 |
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96 | months.set_empty_key(NULL);
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97 | months["january"] = 31;
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98 | months["february"] = 28;
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99 | months["march"] = 31;
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100 | months["april"] = 30;
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101 | months["may"] = 31;
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102 | months["june"] = 30;
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103 | months["july"] = 31;
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104 | months["august"] = 31;
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105 | months["september"] = 30;
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106 | months["october"] = 31;
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107 | months["november"] = 30;
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108 | months["december"] = 31;
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109 |
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110 | cout << "september -> " << months["september"] << endl;
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111 | cout << "april -> " << months["april"] << endl;
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112 | cout << "june -> " << months["june"] << endl;
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113 | cout << "november -> " << months["november"] << endl;
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114 | }
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115 | </pre>
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116 |
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117 |
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118 | <h3>Definition</h3>
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119 |
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120 | Defined in the header <A
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121 | href="dense_hash_map.h">dense_hash_map.h</A>. This class is not
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122 | part of the C++ standard.
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123 |
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124 |
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125 | <h3>Template parameters</h3>
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126 |
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127 | <table border>
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128 | <TR><TH>Parameter</TH><TH>Description</TH><TH>Default</TH></TR>
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129 |
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130 | <TR>
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131 | <TD VAlign=top>
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132 | <tt>Key</tt>
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133 | </TD>
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134 | <TD VAlign=top>
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135 | The hash_map's key type. This is also defined as
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136 | <tt>dense_hash_map::key_type</tt>.
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137 | </TD>
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138 | <TD VAlign=top>
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139 |
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140 | </TD>
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141 | </TR>
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142 |
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143 | <TR>
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144 | <TD VAlign=top>
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145 | <tt>Data</tt>
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146 | </TD>
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147 | <TD VAlign=top>
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148 | The hash_map's data type. This is also defined as
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149 | <tt>dense_hash_map::data_type</tt>.
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150 | </TD>
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151 | <TD VAlign=top>
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152 |
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153 | </TD>
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154 | </TR>
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155 |
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156 | <TR>
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157 | <TD VAlign=top>
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158 | <tt>HashFcn</tt>
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159 | </TD>
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160 | <TD VAlign=top>
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161 | The <A href="http://www.sgi.com/tech/stl/HashFunction.html">hash function</A> used by the
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162 | hash_map. This is also defined as <tt>dense_hash_map::hasher</tt>.
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163 | <br><b>Note:</b> Hashtable performance depends heavliy on the choice of
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164 | hash function. See <A HREF="performance.html#hashfn">the performance
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165 | page</A> for more information.
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166 | </TD>
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167 | <TD VAlign=top>
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168 | <tt><A href="http://www.sgi.com/tech/stl/hash.html">hash</A><Key></tt>
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169 | </TD>
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170 | </TR>
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171 |
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172 | <TR>
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173 | <TD VAlign=top>
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174 | <tt>EqualKey</tt>
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175 | </TD>
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176 | <TD VAlign=top>
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177 | The hash_map key equality function: a <A
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178 | href="http://www.sgi.com/tech/stl/BinaryPredicate.html">binary predicate</A> that determines
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179 | whether two keys are equal. This is also defined as
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180 | <tt>dense_hash_map::key_equal</tt>.
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181 | </TD>
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182 | <TD VAlign=top>
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183 | <tt><A href="http://www.sgi.com/tech/stl/equal_to.html">equal_to</A><Key></tt>
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184 | </TD>
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185 | </TR>
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186 |
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187 | <TR>
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188 | <TD VAlign=top>
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189 | <tt>Alloc</tt>
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190 | </TD>
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191 | <TD VAlign=top>
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192 | <b>Ignored</b>; this is included only for API-compatibility
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193 | with SGI's STL implementation.
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194 | </TD>
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195 | <TD VAlign=top>
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196 | <tt><A href="http://www.sgi.com/tech/stl/Allocators.html">alloc</A></tt>
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197 | </TD>
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198 | </TR>
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199 |
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200 | </table>
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201 |
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202 |
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203 | <h3>Model of</h3>
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204 |
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205 | <A href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique Hashed Associative Container</A>,
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206 | <A href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair Associative Container</A>
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207 |
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208 |
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209 | <h3>Type requirements</h3>
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210 |
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211 | <UL>
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212 | <LI>
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213 | <tt>Key</tt> is Assignable.
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214 | <LI>
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215 | <tt>EqualKey</tt> is a Binary Predicate whose argument type is Key.
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216 | <LI>
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217 | <tt>EqualKey</tt> is an equivalence relation.
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218 | <LI>
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219 | <tt>Alloc</tt> is an Allocator.
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220 | </UL>
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221 |
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222 |
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223 | <h3>Public base classes</h3>
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224 |
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225 | None.
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226 |
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227 |
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228 | <h3>Members</h3>
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229 |
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230 | <table border>
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231 | <TR><TH>Member</TH><TH>Where defined</TH><TH>Description</TH></TR>
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232 |
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233 | <TR>
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234 | <TD VAlign=top>
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235 | <tt>key_type</tt> <A href="#7">[7]</A>
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236 | </TD>
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237 | <TD VAlign=top>
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238 | <A
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239 | href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
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240 | Container</A>
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241 | </TD>
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242 | <TD VAlign=top>
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243 | The <tt>dense_hash_map</tt>'s key type, <tt>Key</tt>.
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244 | </TD>
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245 | </TR>
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246 |
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247 | <TR>
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248 | <TD VAlign=top>
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249 | <tt>data_type</tt> <A href="#7">[7]</A>
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250 | </TD>
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251 | <TD VAlign=top>
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252 | <A
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253 | href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair
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254 | Associative Container</A>
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255 | </TD>
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256 | <TD VAlign=top>
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257 | The type of object associated with the keys.
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258 | </TD>
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259 | </TR>
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260 |
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261 | <TR>
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262 | <TD VAlign=top>
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263 | <tt>value_type</tt>
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264 | </TD>
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265 | <TD VAlign=top>
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266 | <A
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267 | href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair
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268 | Associative Container</A>
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269 | </TD>
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270 | <TD VAlign=top>
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271 | The type of object, <tt>pair<const key_type, data_type></tt>,
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272 | stored in the hash_map.
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273 | </TD>
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274 | </TR>
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275 |
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276 | <TR>
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277 | <TD VAlign=top>
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278 | <tt>hasher</tt>
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279 | </TD>
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280 | <TD VAlign=top>
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281 | <A
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282 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
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283 | Associative Container</A>
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284 | </TD>
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285 | <TD VAlign=top>
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286 | The <tt>dense_hash_map</tt>'s <A
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287 | href="http://www.sgi.com/tech/stl/HashFunction.html">hash
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288 | function</A>.
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289 | </TD>
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290 | </TR>
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291 |
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292 | <TR>
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293 | <TD VAlign=top>
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294 | <tt>key_equal</tt>
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295 | </TD>
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296 | <TD VAlign=top>
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297 | <A
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298 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
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299 | Associative Container</A>
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300 | </TD>
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301 | <TD VAlign=top>
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302 | <A href="http://www.sgi.com/tech/stl/functors.html">Function
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303 | object</A> that compares keys for equality.
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304 | </TD>
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305 | </TR>
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306 |
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307 | <TR>
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308 | <TD VAlign=top>
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309 | <tt>pointer</tt>
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310 | </TD>
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311 | <TD VAlign=top>
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312 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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313 | </TD>
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314 | <TD VAlign=top>
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315 | Pointer to <tt>T</tt>.
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316 | </TD>
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317 | </TR>
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318 |
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319 | <TR>
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320 | <TD VAlign=top>
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321 | <tt>reference</tt>
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322 | </TD>
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323 | <TD VAlign=top>
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324 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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325 | </TD>
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326 | <TD VAlign=top>
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327 | Reference to <tt>T</tt>
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328 | </TD>
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329 | </TR>
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330 |
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331 | <TR>
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332 | <TD VAlign=top>
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333 | <tt>const_reference</tt>
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334 | </TD>
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335 | <TD VAlign=top>
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336 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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337 | </TD>
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338 | <TD VAlign=top>
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339 | Const reference to <tt>T</tt>
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340 | </TD>
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341 | </TR>
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342 |
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343 | <TR>
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344 | <TD VAlign=top>
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345 | <tt>size_type</tt>
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346 | </TD>
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347 | <TD VAlign=top>
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348 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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349 | </TD>
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350 | <TD VAlign=top>
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351 | An unsigned integral type.
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352 | </TD>
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353 | </TR>
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354 |
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355 | <TR>
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356 | <TD VAlign=top>
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357 | <tt>difference_type</tt>
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358 | </TD>
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359 | <TD VAlign=top>
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360 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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361 | </TD>
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362 | <TD VAlign=top>
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363 | A signed integral type.
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364 | </TD>
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365 | </TR>
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366 |
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367 | <TR>
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368 | <TD VAlign=top>
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369 | <tt>iterator</tt>
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370 | </TD>
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371 | <TD VAlign=top>
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372 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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373 | </TD>
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374 | <TD VAlign=top>
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375 | Iterator used to iterate through a <tt>dense_hash_map</tt>. <A
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376 | href="#1">[1]</A>
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377 | </TD>
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378 | </TR>
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379 |
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380 | <TR>
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381 | <TD VAlign=top>
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382 | <tt>const_iterator</tt>
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383 | </TD>
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384 | <TD VAlign=top>
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385 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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386 | </TD>
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387 | <TD VAlign=top>
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388 | Const iterator used to iterate through a <tt>dense_hash_map</tt>.
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389 | </TD>
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390 | </TR>
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391 |
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392 | <TR>
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393 | <TD VAlign=top>
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394 | <tt>iterator begin()</tt>
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395 | </TD>
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396 | <TD VAlign=top>
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397 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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398 | </TD>
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399 | <TD VAlign=top>
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400 | Returns an <tt>iterator</tt> pointing to the beginning of the
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401 | <tt>dense_hash_map</tt>.
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402 | </TD>
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403 | </TR>
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404 |
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405 | <TR>
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406 | <TD VAlign=top>
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407 | <tt>iterator end()</tt>
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408 | </TD>
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409 | <TD VAlign=top>
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410 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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411 | </TD>
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412 | <TD VAlign=top>
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413 | Returns an <tt>iterator</tt> pointing to the end of the
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414 | <tt>dense_hash_map</tt>.
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415 | </TD>
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416 | </TR>
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417 |
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418 | <TR>
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419 | <TD VAlign=top>
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420 | <tt>const_iterator begin() const</tt>
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421 | </TD>
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422 | <TD VAlign=top>
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423 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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424 | </TD>
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425 | <TD VAlign=top>
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426 | Returns an <tt>const_iterator</tt> pointing to the beginning of the
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427 | <tt>dense_hash_map</tt>.
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428 | </TD>
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429 | </TR>
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430 |
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431 | <TR>
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432 | <TD VAlign=top>
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433 | <tt>const_iterator end() const</tt>
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434 | </TD>
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435 | <TD VAlign=top>
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436 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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437 | </TD>
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438 | <TD VAlign=top>
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439 | Returns an <tt>const_iterator</tt> pointing to the end of the
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440 | <tt>dense_hash_map</tt>.
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441 | </TD>
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442 | </TR>
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443 |
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444 | <TR>
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445 | <TD VAlign=top>
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446 | <tt>size_type size() const</tt>
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447 | </TD>
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448 | <TD VAlign=top>
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449 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
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450 | </TD>
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451 | <TD VAlign=top>
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452 | Returns the size of the <tt>dense_hash_map</tt>.
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453 | </TD>
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454 | </TR>
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455 |
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456 | <TR>
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457 | <TD VAlign=top>
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458 | <tt>size_type max_size() const</tt>
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459 | </TD>
|
---|
460 | <TD VAlign=top>
|
---|
461 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
|
---|
462 | </TD>
|
---|
463 | <TD VAlign=top>
|
---|
464 | Returns the largest possible size of the <tt>dense_hash_map</tt>.
|
---|
465 | </TD>
|
---|
466 | </TR>
|
---|
467 |
|
---|
468 | <TR>
|
---|
469 | <TD VAlign=top>
|
---|
470 | <tt>bool empty() const</tt>
|
---|
471 | </TD>
|
---|
472 | <TD VAlign=top>
|
---|
473 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
|
---|
474 | </TD>
|
---|
475 | <TD VAlign=top>
|
---|
476 | <tt>true</tt> if the <tt>dense_hash_map</tt>'s size is <tt>0</tt>.
|
---|
477 | </TD>
|
---|
478 | </TR>
|
---|
479 |
|
---|
480 | <TR>
|
---|
481 | <TD VAlign=top>
|
---|
482 | <tt>size_type bucket_count() const</tt>
|
---|
483 | </TD>
|
---|
484 | <TD VAlign=top>
|
---|
485 | <A
|
---|
486 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
|
---|
487 | Associative Container</A>
|
---|
488 | </TD>
|
---|
489 | <TD VAlign=top>
|
---|
490 | Returns the number of buckets used by the <tt>dense_hash_map</tt>.
|
---|
491 | </TD>
|
---|
492 | </TR>
|
---|
493 |
|
---|
494 | <TR>
|
---|
495 | <TD VAlign=top>
|
---|
496 | <tt>size_type max_bucket_count() const</tt>
|
---|
497 | </TD>
|
---|
498 | <TD VAlign=top>
|
---|
499 | <A
|
---|
500 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
|
---|
501 | Associative Container</A>
|
---|
502 | </TD>
|
---|
503 | <TD VAlign=top>
|
---|
504 | Returns the largest possible number of buckets used by the <tt>dense_hash_map</tt>.
|
---|
505 | </TD>
|
---|
506 | </TR>
|
---|
507 |
|
---|
508 | <TR>
|
---|
509 | <TD VAlign=top>
|
---|
510 | <tt>void resize(size_type n)</tt>
|
---|
511 | </TD>
|
---|
512 | <TD VAlign=top>
|
---|
513 | <A
|
---|
514 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
|
---|
515 | Associative Container</A>
|
---|
516 | </TD>
|
---|
517 | <TD VAlign=top>
|
---|
518 | Increases the bucket count to at least <tt>n</tt>.
|
---|
519 | <A href="#4">[4]</A>
|
---|
520 | </TD>
|
---|
521 | </TR>
|
---|
522 |
|
---|
523 | <TR>
|
---|
524 | <TD VAlign=top>
|
---|
525 | <tt>hasher hash_funct() const</tt>
|
---|
526 | </TD>
|
---|
527 | <TD VAlign=top>
|
---|
528 | <A
|
---|
529 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
|
---|
530 | Associative Container</A>
|
---|
531 | </TD>
|
---|
532 | <TD VAlign=top>
|
---|
533 | Returns the <tt>hasher</tt> object used by the <tt>dense_hash_map</tt>.
|
---|
534 | </TD>
|
---|
535 | </TR>
|
---|
536 |
|
---|
537 | <TR>
|
---|
538 | <TD VAlign=top>
|
---|
539 | <tt>key_equal key_eq() const</tt>
|
---|
540 | </TD>
|
---|
541 | <TD VAlign=top>
|
---|
542 | <A
|
---|
543 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
|
---|
544 | Associative Container</A>
|
---|
545 | </TD>
|
---|
546 | <TD VAlign=top>
|
---|
547 | Returns the <tt>key_equal</tt> object used by the
|
---|
548 | <tt>dense_hash_map</tt>.
|
---|
549 | </TD>
|
---|
550 | </TR>
|
---|
551 |
|
---|
552 | <TR>
|
---|
553 | <TD VAlign=top>
|
---|
554 | <tt>dense_hash_map()</tt>
|
---|
555 | </TD>
|
---|
556 | <TD VAlign=top>
|
---|
557 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
|
---|
558 | </TD>
|
---|
559 | <TD VAlign=top>
|
---|
560 | Creates an empty <tt>dense_hash_map</tt>.
|
---|
561 | </TD>
|
---|
562 | </TR>
|
---|
563 |
|
---|
564 | <TR>
|
---|
565 | <TD VAlign=top>
|
---|
566 | <tt>dense_hash_map(size_type n)</tt>
|
---|
567 | </TD>
|
---|
568 | <TD VAlign=top>
|
---|
569 | <A
|
---|
570 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
|
---|
571 | Associative Container</A>
|
---|
572 | </TD>
|
---|
573 | <TD VAlign=top>
|
---|
574 | Creates an empty <tt>dense_hash_map</tt> that's optimized for holding
|
---|
575 | up to <tt>n</tt> items.
|
---|
576 | <A href="#5">[5]</A>
|
---|
577 | </TD>
|
---|
578 | </TR>
|
---|
579 |
|
---|
580 | <TR>
|
---|
581 | <TD VAlign=top>
|
---|
582 | <tt>dense_hash_map(size_type n, const hasher& h)</tt>
|
---|
583 | </TD>
|
---|
584 | <TD VAlign=top>
|
---|
585 | <A
|
---|
586 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
|
---|
587 | Associative Container</A>
|
---|
588 | </TD>
|
---|
589 | <TD VAlign=top>
|
---|
590 | Creates an empty <tt>dense_hash_map</tt> that's optimized for up
|
---|
591 | to <tt>n</tt> items, using <tt>h</tt> as the hash function.
|
---|
592 | </TD>
|
---|
593 | </TR>
|
---|
594 |
|
---|
595 | <TR>
|
---|
596 | <TD VAlign=top>
|
---|
597 | <tt>dense_hash_map(size_type n, const hasher& h, const
|
---|
598 | key_equal& k)</tt>
|
---|
599 | </TD>
|
---|
600 | <TD VAlign=top>
|
---|
601 | <A
|
---|
602 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
|
---|
603 | Associative Container</A>
|
---|
604 | </TD>
|
---|
605 | <TD VAlign=top>
|
---|
606 | Creates an empty <tt>dense_hash_map</tt> that's optimized for up
|
---|
607 | to <tt>n</tt> items, using <tt>h</tt> as the hash function and
|
---|
608 | <tt>k</tt> as the key equal function.
|
---|
609 | </TD>
|
---|
610 | </TR>
|
---|
611 |
|
---|
612 | <TR>
|
---|
613 | <TD VAlign=top>
|
---|
614 | <pre>template <class <A
|
---|
615 | href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</A>>
|
---|
616 | dense_hash_map(InputIterator f, InputIterator l) </pre>
|
---|
617 | <A href="#2">[2]</A>
|
---|
618 | </TD>
|
---|
619 | <TD VAlign=top>
|
---|
620 | <A
|
---|
621 | href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique
|
---|
622 | Hashed Associative Container</A>
|
---|
623 | </TD>
|
---|
624 | <TD VAlign=top>
|
---|
625 | Creates a dense_hash_map with a copy of a range.
|
---|
626 | </TD>
|
---|
627 | </TR>
|
---|
628 |
|
---|
629 | <TR>
|
---|
630 | <TD VAlign=top>
|
---|
631 | <pre>template <class <A
|
---|
632 | href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</A>>
|
---|
633 | dense_hash_map(InputIterator f, InputIterator l, size_type n) </pre>
|
---|
634 | <A href="#2">[2]</A>
|
---|
635 | </TD>
|
---|
636 | <TD VAlign=top>
|
---|
637 | <A
|
---|
638 | href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique
|
---|
639 | Hashed Associative Container</A>
|
---|
640 | </TD>
|
---|
641 | <TD VAlign=top>
|
---|
642 | Creates a hash_map with a copy of a range that's optimized to
|
---|
643 | hold up to <tt>n</tt> items.
|
---|
644 | </TD>
|
---|
645 | </TR>
|
---|
646 |
|
---|
647 | <TR>
|
---|
648 | <TD VAlign=top>
|
---|
649 | <pre>template <class <A
|
---|
650 | href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</A>>
|
---|
651 | dense_hash_map(InputIterator f, InputIterator l, size_type n, const
|
---|
652 | hasher& h) </pre> <A href="#2">[2]</A>
|
---|
653 | </TD>
|
---|
654 | <TD VAlign=top>
|
---|
655 | <A
|
---|
656 | href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique
|
---|
657 | Hashed Associative Container</A>
|
---|
658 | </TD>
|
---|
659 | <TD VAlign=top>
|
---|
660 | Creates a hash_map with a copy of a range that's optimized to hold
|
---|
661 | up to <tt>n</tt> items, using <tt>h</tt> as the hash function.
|
---|
662 | </TD>
|
---|
663 | </TR>
|
---|
664 |
|
---|
665 | <TR>
|
---|
666 | <TD VAlign=top>
|
---|
667 | <pre>template <class <A
|
---|
668 | href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</A>>
|
---|
669 | dense_hash_map(InputIterator f, InputIterator l, size_type n, const
|
---|
670 | hasher& h, const key_equal& k) </pre> <A href="#2">[2]</A>
|
---|
671 | </TD>
|
---|
672 | <TD VAlign=top>
|
---|
673 | <A
|
---|
674 | href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique
|
---|
675 | Hashed Associative Container</A>
|
---|
676 | </TD>
|
---|
677 | <TD VAlign=top>
|
---|
678 | Creates a hash_map with a copy of a range that's optimized for
|
---|
679 | holding up to <tt>n</tt> items, using <tt>h</tt> as the hash
|
---|
680 | function and <tt>k</tt> as the key equal function.
|
---|
681 | </TD>
|
---|
682 | </TR>
|
---|
683 |
|
---|
684 | <TR>
|
---|
685 | <TD VAlign=top>
|
---|
686 | <tt>dense_hash_map(const hash_map&)</tt>
|
---|
687 | </TD>
|
---|
688 | <TD VAlign=top>
|
---|
689 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
|
---|
690 | </TD>
|
---|
691 | <TD VAlign=top>
|
---|
692 | The copy constructor.
|
---|
693 | </TD>
|
---|
694 | </TR>
|
---|
695 |
|
---|
696 | <TR>
|
---|
697 | <TD VAlign=top>
|
---|
698 | <tt>dense_hash_map& operator=(const hash_map&)</tt>
|
---|
699 | </TD>
|
---|
700 | <TD VAlign=top>
|
---|
701 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
|
---|
702 | </TD>
|
---|
703 | <TD VAlign=top>
|
---|
704 | The assignment operator
|
---|
705 | </TD>
|
---|
706 | </TR>
|
---|
707 |
|
---|
708 | <TR>
|
---|
709 | <TD VAlign=top>
|
---|
710 | <tt>void swap(hash_map&)</tt>
|
---|
711 | </TD>
|
---|
712 | <TD VAlign=top>
|
---|
713 | <A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
|
---|
714 | </TD>
|
---|
715 | <TD VAlign=top>
|
---|
716 | Swaps the contents of two hash_maps.
|
---|
717 | </TD>
|
---|
718 | </TR>
|
---|
719 |
|
---|
720 | <TR>
|
---|
721 | <TD VAlign=top>
|
---|
722 | <pre>pair<iterator, bool> insert(const value_type& x)
|
---|
723 | </pre>
|
---|
724 | </TD>
|
---|
725 | <TD VAlign=top>
|
---|
726 | <A
|
---|
727 | href="http://www.sgi.com/tech/stl/UniqueAssociativeContainer.html">Unique
|
---|
728 | Associative Container</A>
|
---|
729 | </TD>
|
---|
730 | <TD VAlign=top>
|
---|
731 | Inserts <tt>x</tt> into the <tt>dense_hash_map</tt>.
|
---|
732 | </TD>
|
---|
733 | </TR>
|
---|
734 |
|
---|
735 | <TR>
|
---|
736 | <TD VAlign=top>
|
---|
737 | <pre>template <class <A
|
---|
738 | href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</A>>
|
---|
739 | void insert(InputIterator f, InputIterator l) </pre> <A href="#2">[2]</A>
|
---|
740 | </TD>
|
---|
741 | <TD VAlign=top>
|
---|
742 | <A
|
---|
743 | href="http://www.sgi.com/tech/stl/UniqueAssociativeContainer.html">Unique
|
---|
744 | Associative Container</A>
|
---|
745 | </TD>
|
---|
746 | <TD VAlign=top>
|
---|
747 | Inserts a range into the <tt>dense_hash_map</tt>.
|
---|
748 | </TD>
|
---|
749 | </TR>
|
---|
750 |
|
---|
751 | <TR>
|
---|
752 | <TD VAlign=top>
|
---|
753 | <tt>void set_empty_key(const key_type& key)</tt> <A href="#6">[6]</A>
|
---|
754 | </TD>
|
---|
755 | <TD VAlign=top>
|
---|
756 | <tt>dense_hash_map</tt>
|
---|
757 | </TD>
|
---|
758 | <TD VAlign=top>
|
---|
759 | See below.
|
---|
760 | </TD>
|
---|
761 | </TR>
|
---|
762 |
|
---|
763 | <TR>
|
---|
764 | <TD VAlign=top>
|
---|
765 | <tt>void set_deleted_key(const key_type& key)</tt> <A href="#6">[6]</A>
|
---|
766 | </TD>
|
---|
767 | <TD VAlign=top>
|
---|
768 | <tt>dense_hash_map</tt>
|
---|
769 | </TD>
|
---|
770 | <TD VAlign=top>
|
---|
771 | See below.
|
---|
772 | </TD>
|
---|
773 | </TR>
|
---|
774 |
|
---|
775 | <TR>
|
---|
776 | <TD VAlign=top>
|
---|
777 | <tt>void clear_deleted_key()</tt> <A href="#6">[6]</A>
|
---|
778 | </TD>
|
---|
779 | <TD VAlign=top>
|
---|
780 | <tt>dense_hash_map</tt>
|
---|
781 | </TD>
|
---|
782 | <TD VAlign=top>
|
---|
783 | See below.
|
---|
784 | </TD>
|
---|
785 | </TR>
|
---|
786 |
|
---|
787 | <TR>
|
---|
788 | <TD VAlign=top>
|
---|
789 | <tt>void erase(iterator pos)</tt>
|
---|
790 | </TD>
|
---|
791 | <TD VAlign=top>
|
---|
792 | <A
|
---|
793 | href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
|
---|
794 | Container</A>
|
---|
795 | </TD>
|
---|
796 | <TD VAlign=top>
|
---|
797 | Erases the element pointed to by <tt>pos</tt>.
|
---|
798 | <A href="#6">[6]</A>
|
---|
799 | </TD>
|
---|
800 | </TR>
|
---|
801 |
|
---|
802 | <TR>
|
---|
803 | <TD VAlign=top>
|
---|
804 | <tt>size_type erase(const key_type& k)</tt>
|
---|
805 | </TD>
|
---|
806 | <TD VAlign=top>
|
---|
807 | <A
|
---|
808 | href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
|
---|
809 | Container</A>
|
---|
810 | </TD>
|
---|
811 | <TD VAlign=top>
|
---|
812 | Erases the element whose key is <tt>k</tt>.
|
---|
813 | <A href="#6">[6]</A>
|
---|
814 | </TD>
|
---|
815 | </TR>
|
---|
816 |
|
---|
817 | <TR>
|
---|
818 | <TD VAlign=top>
|
---|
819 | <tt>void erase(iterator first, iterator last)</tt>
|
---|
820 | </TD>
|
---|
821 | <TD VAlign=top>
|
---|
822 | <A
|
---|
823 | href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
|
---|
824 | Container</A>
|
---|
825 | </TD>
|
---|
826 | <TD VAlign=top>
|
---|
827 | Erases all elements in a range.
|
---|
828 | <A href="#6">[6]</A>
|
---|
829 | </TD>
|
---|
830 | </TR>
|
---|
831 |
|
---|
832 | <TR>
|
---|
833 | <TD VAlign=top>
|
---|
834 | <tt>void clear()</tt>
|
---|
835 | </TD>
|
---|
836 | <TD VAlign=top>
|
---|
837 | <A
|
---|
838 | href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
|
---|
839 | Container</A>
|
---|
840 | </TD>
|
---|
841 | <TD VAlign=top>
|
---|
842 | Erases all of the elements.
|
---|
843 | </TD>
|
---|
844 | </TR>
|
---|
845 |
|
---|
846 | <TR>
|
---|
847 | <TD VAlign=top>
|
---|
848 | <tt>const_iterator find(const key_type& k) const</tt>
|
---|
849 | </TD>
|
---|
850 | <TD VAlign=top>
|
---|
851 | <A
|
---|
852 | href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
|
---|
853 | Container</A>
|
---|
854 | </TD>
|
---|
855 | <TD VAlign=top>
|
---|
856 | Finds an element whose key is <tt>k</tt>.
|
---|
857 | </TD>
|
---|
858 | </TR>
|
---|
859 |
|
---|
860 | <TR>
|
---|
861 | <TD VAlign=top>
|
---|
862 | <tt>iterator find(const key_type& k)</tt>
|
---|
863 | </TD>
|
---|
864 | <TD VAlign=top>
|
---|
865 | <A
|
---|
866 | href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
|
---|
867 | Container</A>
|
---|
868 | </TD>
|
---|
869 | <TD VAlign=top>
|
---|
870 | Finds an element whose key is <tt>k</tt>.
|
---|
871 | </TD>
|
---|
872 | </TR>
|
---|
873 |
|
---|
874 | <TR>
|
---|
875 | <TD VAlign=top>
|
---|
876 | <tt>size_type count(const key_type& k) const</tt>
|
---|
877 | </TD>
|
---|
878 | <TD VAlign=top>
|
---|
879 | <A
|
---|
880 | href="http://www.sgi.com/tech/stl/UniqueAssociativeContainer.html">Unique
|
---|
881 | Associative Container</A>
|
---|
882 | </TD>
|
---|
883 | <TD VAlign=top>
|
---|
884 | Counts the number of elements whose key is <tt>k</tt>.
|
---|
885 | </TD>
|
---|
886 | </TR>
|
---|
887 |
|
---|
888 | <TR>
|
---|
889 | <TD VAlign=top>
|
---|
890 | <pre>pair<const_iterator, const_iterator> equal_range(const
|
---|
891 | key_type& k) const </pre>
|
---|
892 | </TD>
|
---|
893 | <TD VAlign=top>
|
---|
894 | <A
|
---|
895 | href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
|
---|
896 | Container</A>
|
---|
897 | </TD>
|
---|
898 | <TD VAlign=top>
|
---|
899 | Finds a range containing all elements whose key is <tt>k</tt>.
|
---|
900 | </TD>
|
---|
901 | </TR>
|
---|
902 |
|
---|
903 | <TR>
|
---|
904 | <TD VAlign=top>
|
---|
905 | <pre>pair<iterator, iterator> equal_range(const
|
---|
906 | key_type& k) </pre>
|
---|
907 | </TD>
|
---|
908 | <TD VAlign=top>
|
---|
909 | <A
|
---|
910 | href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
|
---|
911 | Container</A>
|
---|
912 | </TD>
|
---|
913 | <TD VAlign=top>
|
---|
914 | Finds a range containing all elements whose key is <tt>k</tt>.
|
---|
915 | </TD>
|
---|
916 | </TR>
|
---|
917 |
|
---|
918 | <TR>
|
---|
919 | <TD VAlign=top>
|
---|
920 | <pre>data_type& operator[](const key_type& k) <A
|
---|
921 | href="http://www.sgi.com/tech/stl/#3">[3]</A> </pre>
|
---|
922 | </TD>
|
---|
923 | <TD VAlign=top>
|
---|
924 | <tt>dense_hash_map</tt>
|
---|
925 | </TD>
|
---|
926 | <TD VAlign=top>
|
---|
927 | See below.
|
---|
928 | </TD>
|
---|
929 | </TR>
|
---|
930 |
|
---|
931 | <TR>
|
---|
932 | <TD VAlign=top>
|
---|
933 | <tt>bool write_metadata(FILE *fp)</tt>
|
---|
934 | </TD>
|
---|
935 | <TD VAlign=top>
|
---|
936 | <tt>dense_hash_map</tt>
|
---|
937 | </TD>
|
---|
938 | <TD VAlign=top>
|
---|
939 | See below.
|
---|
940 | </TD>
|
---|
941 | </TR>
|
---|
942 |
|
---|
943 | <TR>
|
---|
944 | <TD VAlign=top>
|
---|
945 | <tt>bool read_metadata(FILE *fp)</tt>
|
---|
946 | </TD>
|
---|
947 | <TD VAlign=top>
|
---|
948 | <tt>dense_hash_map</tt>
|
---|
949 | </TD>
|
---|
950 | <TD VAlign=top>
|
---|
951 | See below.
|
---|
952 | </TD>
|
---|
953 | </TR>
|
---|
954 |
|
---|
955 | <TR>
|
---|
956 | <TD VAlign=top>
|
---|
957 | <tt>bool write_nopointer_data(FILE *fp)</tt>
|
---|
958 | </TD>
|
---|
959 | <TD VAlign=top>
|
---|
960 | <tt>dense_hash_map</tt>
|
---|
961 | </TD>
|
---|
962 | <TD VAlign=top>
|
---|
963 | See below.
|
---|
964 | </TD>
|
---|
965 | </TR>
|
---|
966 |
|
---|
967 | <TR>
|
---|
968 | <TD VAlign=top>
|
---|
969 | <tt>bool read_nopointer_data(FILE *fp)</tt>
|
---|
970 | </TD>
|
---|
971 | <TD VAlign=top>
|
---|
972 | <tt>dense_hash_map</tt>
|
---|
973 | </TD>
|
---|
974 | <TD VAlign=top>
|
---|
975 | See below.
|
---|
976 | </TD>
|
---|
977 | </TR>
|
---|
978 |
|
---|
979 | <TR>
|
---|
980 | <TD VAlign=top>
|
---|
981 | <pre>bool operator==(const hash_map&, const hash_map&)
|
---|
982 | </pre>
|
---|
983 | </TD>
|
---|
984 | <TD VAlign=top>
|
---|
985 | <A
|
---|
986 | href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
|
---|
987 | Associative Container</A>
|
---|
988 | </TD>
|
---|
989 | <TD VAlign=top>
|
---|
990 | Tests two hash_maps for equality. This is a global function, not a
|
---|
991 | member function.
|
---|
992 | </TD>
|
---|
993 | </TR>
|
---|
994 |
|
---|
995 | </table>
|
---|
996 |
|
---|
997 |
|
---|
998 | <h3>New members</h3>
|
---|
999 |
|
---|
1000 | These members are not defined in the <A
|
---|
1001 | href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique
|
---|
1002 | Hashed Associative Container</A> and <A
|
---|
1003 | href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair
|
---|
1004 | Associative Container</A> requirements, but are specific to
|
---|
1005 | <tt>dense_hash_map</tt>.
|
---|
1006 |
|
---|
1007 | <table border>
|
---|
1008 | <TR><TH>Member</TH><TH>Description</TH></TR>
|
---|
1009 |
|
---|
1010 | <TR>
|
---|
1011 | <TD VAlign=top>
|
---|
1012 | <tt>void set_empty_key(const key_type& key)</tt>
|
---|
1013 | </TD>
|
---|
1014 | <TD VAlign=top>
|
---|
1015 | Sets the distinguished "empty" key to <tt>key</tt>. This must be
|
---|
1016 | called immediately after construct time, before calls to another
|
---|
1017 | other <tt>dense_hash_map</tt> operation. <A href="#6">[6]</A>
|
---|
1018 | </TD>
|
---|
1019 | </TR>
|
---|
1020 |
|
---|
1021 | <TR>
|
---|
1022 | <TD VAlign=top>
|
---|
1023 | <tt>void set_deleted_key(const key_type& key)</tt>
|
---|
1024 | </TD>
|
---|
1025 | <TD VAlign=top>
|
---|
1026 | Sets the distinguished "deleted" key to <tt>key</tt>. This must be
|
---|
1027 | called before any calls to <tt>erase()</tt>. <A href="#6">[6]</A>
|
---|
1028 | </TD>
|
---|
1029 | </TR>
|
---|
1030 |
|
---|
1031 | <TR>
|
---|
1032 | <TD VAlign=top>
|
---|
1033 | <tt>void clear_deleted_key()</tt> <A href="#6">[6]</A>
|
---|
1034 | </TD>
|
---|
1035 | <TD VAlign=top>
|
---|
1036 | Clears the distinguished "deleted" key. After this is called,
|
---|
1037 | calls to <tt>erase()</tt> are not valid on this object.
|
---|
1038 | <A href="#6">[6]</A>
|
---|
1039 | </TD>
|
---|
1040 | </TR>
|
---|
1041 |
|
---|
1042 | <TR>
|
---|
1043 | <TD VAlign=top>
|
---|
1044 | <pre>
|
---|
1045 | data_type&
|
---|
1046 | operator[](const key_type& k) <A
|
---|
1047 | href="http://www.sgi.com/tech/stl/#3">[3]</A>
|
---|
1048 | </pre>
|
---|
1049 | </TD>
|
---|
1050 | <TD VAlign=top>
|
---|
1051 | Returns a reference to the object that is associated with
|
---|
1052 | a particular key. If the <tt>dense_hash_map</tt> does not already
|
---|
1053 | contain such an object, <tt>operator[]</tt> inserts the default
|
---|
1054 | object <tt>data_type()</tt>. <A
|
---|
1055 | href="http://www.sgi.com/tech/stl/#3">[3]</A>
|
---|
1056 | </TD>
|
---|
1057 | </TR>
|
---|
1058 |
|
---|
1059 | <TR>
|
---|
1060 | <TD VAlign=top>
|
---|
1061 | <tt>bool write_metadata(FILE *fp)</tt>
|
---|
1062 | </TD>
|
---|
1063 | <TD VAlign=top>
|
---|
1064 | Write hashtable metadata to <tt>fp</tt>. See <A HREF="#io">below</A>.
|
---|
1065 | </TD>
|
---|
1066 | </TR>
|
---|
1067 |
|
---|
1068 | <TR>
|
---|
1069 | <TD VAlign=top>
|
---|
1070 | <tt>bool read_metadata(FILE *fp)</tt>
|
---|
1071 | </TD>
|
---|
1072 | <TD VAlign=top>
|
---|
1073 | Read hashtable metadata from <tt>fp</tt>. See <A HREF="#io">below</A>.
|
---|
1074 | </TD>
|
---|
1075 | </TR>
|
---|
1076 |
|
---|
1077 | <TR>
|
---|
1078 | <TD VAlign=top>
|
---|
1079 | <tt>bool write_nopointer_data(FILE *fp)</tt>
|
---|
1080 | </TD>
|
---|
1081 | <TD VAlign=top>
|
---|
1082 | Write hashtable contents to <tt>fp</tt>. This is valid only if the
|
---|
1083 | hashtable key and value are "plain" data. See <A HREF="#io">below</A>.
|
---|
1084 | </TD>
|
---|
1085 | </TR>
|
---|
1086 |
|
---|
1087 | <TR>
|
---|
1088 | <TD VAlign=top>
|
---|
1089 | <tt>bool read_nopointer_data(FILE *fp)</tt>
|
---|
1090 | </TD>
|
---|
1091 | <TD VAlign=top>
|
---|
1092 | Read hashtable contents to <tt>fp</tt>. This is valid only if the
|
---|
1093 | hashtable key and value are "plain" data. See <A HREF="#io">below</A>.
|
---|
1094 | </TD>
|
---|
1095 | </TR>
|
---|
1096 |
|
---|
1097 | </table>
|
---|
1098 |
|
---|
1099 |
|
---|
1100 | <h3>Notes</h3>
|
---|
1101 |
|
---|
1102 | <P><A name="1">[1]</A>
|
---|
1103 |
|
---|
1104 | <tt>dense_hash_map::iterator</tt> is not a mutable iterator, because
|
---|
1105 | <tt>dense_hash_map::value_type</tt> is not <A
|
---|
1106 | href="http://www.sgi.com/tech/stl/Assignable.html">Assignable</A>.
|
---|
1107 | That is, if <tt>i</tt> is of type <tt>dense_hash_map::iterator</tt>
|
---|
1108 | and <tt>p</tt> is of type <tt>dense_hash_map::value_type</tt>, then
|
---|
1109 | <tt>*i = p</tt> is not a valid expression. However,
|
---|
1110 | <tt>dense_hash_map::iterator</tt> isn't a constant iterator either,
|
---|
1111 | because it can be used to modify the object that it points to. Using
|
---|
1112 | the same notation as above, <tt>(*i).second = p</tt> is a valid
|
---|
1113 | expression.</p>
|
---|
1114 |
|
---|
1115 | <P><A name="2">[2]</A>
|
---|
1116 |
|
---|
1117 | This member function relies on <i>member template</i> functions, which
|
---|
1118 | may not be supported by all compilers. If your compiler supports
|
---|
1119 | member templates, you can call this function with any type of <A
|
---|
1120 | href="http://www.sgi.com/tech/stl/InputIterator.html">input
|
---|
1121 | iterator</A>. If your compiler does not yet support member templates,
|
---|
1122 | though, then the arguments must either be of type <tt>const
|
---|
1123 | value_type*</tt> or of type <tt>dense_hash_map::const_iterator</tt>.</p>
|
---|
1124 |
|
---|
1125 | <P><A name="3">[3]</A>
|
---|
1126 |
|
---|
1127 | Since <tt>operator[]</tt> might insert a new element into the
|
---|
1128 | <tt>dense_hash_map</tt>, it can't possibly be a <tt>const</tt> member
|
---|
1129 | function. Note that the definition of <tt>operator[]</tt> is
|
---|
1130 | extremely simple: <tt>m[k]</tt> is equivalent to
|
---|
1131 | <tt>(*((m.insert(value_type(k, data_type()))).first)).second</tt>.
|
---|
1132 | Strictly speaking, this member function is unnecessary: it exists only
|
---|
1133 | for convenience.</p>
|
---|
1134 |
|
---|
1135 | <P><A name="4">[4]</A>
|
---|
1136 |
|
---|
1137 | In order to preserve iterators, erasing hashtable elements does not
|
---|
1138 | cause a hashtable to resize. This means that after a string of
|
---|
1139 | <tt>erase()</tt> calls, the hashtable will use more space than is
|
---|
1140 | required. At a cost of invalidating all current iterators, you can
|
---|
1141 | call <tt>resize()</tt> to manually compact the hashtable. The
|
---|
1142 | hashtable promotes too-small <tt>resize()</tt> arguments to the
|
---|
1143 | smallest legal value, so to compact a hashtable, it's sufficient to
|
---|
1144 | call <tt>resize(0)</tt>.
|
---|
1145 |
|
---|
1146 | <P><A name="5">[5]</A>
|
---|
1147 |
|
---|
1148 | Unlike some other hashtable implementations, the optional <i>n</i> in
|
---|
1149 | the constructor size indicates not the desired number of buckets that
|
---|
1150 | should be allocated, but instead the expected number of items to be
|
---|
1151 | inserted. The class then sizes the hash-map appropriately for the
|
---|
1152 | number of items specified. It's not an error to actually insert more
|
---|
1153 | or fewer items into the hashtable, but the implementation is most
|
---|
1154 | efficient -- does the fewest hashtable resizes -- if the number of
|
---|
1155 | inserted items is close to <i>n</i>.</p>
|
---|
1156 |
|
---|
1157 | <P><A name="6">[6]</A>
|
---|
1158 |
|
---|
1159 | <tt>dense_hash_map</tt> <b>requires</b> you call
|
---|
1160 | <tt>set_empty_key()</tt> immediately after constructing the hash-map,
|
---|
1161 | and before calling any other <tt>dense_hash_map</tt> method. (This is
|
---|
1162 | the largest difference between the <tt>dense_hash_map</tt> API and
|
---|
1163 | other hash-map APIs. See <A HREF="implementation.html">implementation.html</A>
|
---|
1164 | for why this is necessary.)
|
---|
1165 | The argument to <tt>set_empty_key()</tt> should be a key-value that
|
---|
1166 | is never used for legitimate hash-map entries. If you have no such
|
---|
1167 | key value, you will be unable to use <tt>dense_hash_map</tt>. It is
|
---|
1168 | an error to call <tt>insert()</tt> with an item whose key is the
|
---|
1169 | "empty key."</p>
|
---|
1170 |
|
---|
1171 | <tt>dense_hash_map</tt> also requires you call
|
---|
1172 | <tt>set_deleted_key()</tt> before calling <tt>erase()</tt>.
|
---|
1173 | The argument to <tt>set_deleted_key()</tt> should be a key-value that
|
---|
1174 | is never used for legitimate hash-map entries. It must be different
|
---|
1175 | from the key-value used for <tt>set_empty_key()</tt>. It is an error to call
|
---|
1176 | <tt>erase()</tt> without first calling <tt>set_deleted_key()</tt>, and
|
---|
1177 | it is also an error to call <tt>insert()</tt> with an item whose key
|
---|
1178 | is the "deleted key."</p>
|
---|
1179 |
|
---|
1180 | <p>There is no need to call <tt>set_deleted_key</tt> if you do not
|
---|
1181 | wish to call <tt>erase()</tt> on the hash-map.</p>
|
---|
1182 |
|
---|
1183 | <p>It is acceptable to change the deleted-key at any time by calling
|
---|
1184 | <tt>set_deleted_key()</tt> with a new argument. You can also call
|
---|
1185 | <tt>clear_deleted_key()</tt>, at which point all keys become valid for
|
---|
1186 | insertion but no hashtable entries can be deleted until
|
---|
1187 | <tt>set_deleted_key()</tt> is called again.</p>
|
---|
1188 |
|
---|
1189 | <P><A name="7">[7]</A>
|
---|
1190 |
|
---|
1191 | Both <tt>key_type</tt> and <tt>data_type</tt> must be <A
|
---|
1192 | HREF="http://c2.com/cgi/wiki?PlainOldData">plain old data</A> (see
|
---|
1193 | <A HREF="implementation.html">implementation.html</A> for why this is
|
---|
1194 | necessary). In addition, there should
|
---|
1195 | be no data structures that point directly into parts of key or value,
|
---|
1196 | including the key or value itself (for instance, you cannot have a
|
---|
1197 | value like <tt>struct {int a = 1, *b = &a}</tt>. This is because
|
---|
1198 | <tt>dense_hash_map</tt> uses <tt>malloc()</tt> and <tt>free()</tt> to
|
---|
1199 | allocate space for the key and value, and <tt>memmove()</tt> to
|
---|
1200 | reorganize the key and value in memory.</p>
|
---|
1201 |
|
---|
1202 | <p>Almost all common uses fit this criterion: <tt>key_type</tt> can be
|
---|
1203 | a basic C type or an STL type like <tt>string</tt>, for instance. If
|
---|
1204 | <tt>value_type</tt> is complex, consider storing only the pointer to
|
---|
1205 | the data in the <tt>dense_hash_map</tt>. This will speed up the
|
---|
1206 | hashtable as well, since hashtable resizes will have to manipulate
|
---|
1207 | less memory.</p>
|
---|
1208 |
|
---|
1209 |
|
---|
1210 | <h3><A NAME=io>Input/Output</A></h3>
|
---|
1211 |
|
---|
1212 | <table border=1 cellpadding=5><tr><td>
|
---|
1213 | <p><b>IMPORTANT IMPLEMENTATION NOTE:</b> In the current version of
|
---|
1214 | this code, the input/output routines for <tt>dense_hash_map</tt> have
|
---|
1215 | <b>not yet been implemented</b>. This section explains the API, but
|
---|
1216 | note that all calls to these routines will fail (return
|
---|
1217 | <tt>false</tt>). It is a TODO to remedy this situation.</p>
|
---|
1218 | </td></tr></table>
|
---|
1219 |
|
---|
1220 | <p>It is possible to save and restore <tt>dense_hash_map</tt> objects
|
---|
1221 | to disk. Storage takes place in two steps. The first writes the
|
---|
1222 | hashtable metadata. The second writes the actual data.</p>
|
---|
1223 |
|
---|
1224 | <p>To write a hashtable to disk, first call <tt>write_metadata()</tt>
|
---|
1225 | on an open file pointer. This saves the hashtable information in a
|
---|
1226 | byte-order-independent format.</p>
|
---|
1227 |
|
---|
1228 | <p>After the metadata has been written to disk, you must write the
|
---|
1229 | actual data stored in the hash-map to disk. If both the key and data
|
---|
1230 | are "simple" enough, you can do this by calling
|
---|
1231 | <tt>write_nopointer_data()</tt>. "Simple" data is data that can be
|
---|
1232 | safely copied to disk via <tt>fwrite()</tt>. Native C data types fall
|
---|
1233 | into this category, as do structs of native C data types. Pointers
|
---|
1234 | and STL objects do not.</p>
|
---|
1235 |
|
---|
1236 | <p>Note that <tt>write_nopointer_data()</tt> does not do any endian
|
---|
1237 | conversion. Thus, it is only appropriate when you intend to read the
|
---|
1238 | data on the same endian architecture as you write the data.</p>
|
---|
1239 |
|
---|
1240 | <p>If you cannot use <tt>write_nopointer_data()</tt> for any reason,
|
---|
1241 | you can write the data yourself by iterating over the
|
---|
1242 | <tt>dense_hash_map</tt> with a <tt>const_iterator</tt> and writing
|
---|
1243 | the key and data in any manner you wish.</p>
|
---|
1244 |
|
---|
1245 | <p>To read the hashtable information from disk, first you must create
|
---|
1246 | a <tt>dense_hash_map</tt> object. Then open a file pointer to point
|
---|
1247 | to the saved hashtable, and call <tt>read_metadata()</tt>. If you
|
---|
1248 | saved the data via <tt>write_nopointer_data()</tt>, you can follow the
|
---|
1249 | <tt>read_metadata()</tt> call with a call to
|
---|
1250 | <tt>read_nopointer_data()</tt>. This is all that is needed.</p>
|
---|
1251 |
|
---|
1252 | <p>If you saved the data through a custom write routine, you must call
|
---|
1253 | a custom read routine to read in the data. To do this, iterate over
|
---|
1254 | the <tt>dense_hash_map</tt> with an <tt>iterator</tt>; this operation
|
---|
1255 | is sensical because the metadata has already been set up. For each
|
---|
1256 | iterator item, you can read the key and value from disk, and set it
|
---|
1257 | appropriately. You will need to do a <tt>const_cast</tt> on the
|
---|
1258 | iterator, since <tt>it->first</tt> is always <tt>const</tt>. The
|
---|
1259 | code might look like this:</p>
|
---|
1260 | <pre>
|
---|
1261 | for (dense_hash_map<int*, int>::iterator it = ht.begin();
|
---|
1262 | it != ht.end(); ++it) {
|
---|
1263 | const_cast<int*>(it->first) = new int;
|
---|
1264 | fread(const_cast<int*>(it->first), sizeof(int), 1, fp);
|
---|
1265 | fread(&it->second, sizeof(int), 1, fp);
|
---|
1266 | }
|
---|
1267 | </pre>
|
---|
1268 |
|
---|
1269 |
|
---|
1270 | <h3><A NAME=iter>Validity of Iterators</A></h3>
|
---|
1271 |
|
---|
1272 | <p><tt>insert()</tt> invalidates all iterators, as does
|
---|
1273 | <tt>resize()</tt>. <tt>erase()</tt> is guaranteed not to invalidate
|
---|
1274 | any iterators.</p>
|
---|
1275 |
|
---|
1276 | <p>This is implemented by making <tt>erase()</tt> not resize the
|
---|
1277 | hashtable. If you desire maximum space efficiency, you can call
|
---|
1278 | <tt>resize(0)</tt> after a string of <tt>erase()</tt> calls, to force
|
---|
1279 | the hashtable to resize to the smallest possible size.</p>
|
---|
1280 |
|
---|
1281 |
|
---|
1282 | <h3>See also</h3>
|
---|
1283 |
|
---|
1284 | <p>The following are SGI STL concepts and classes related to
|
---|
1285 | <tt>dense_hash_map</tt>.</p>
|
---|
1286 |
|
---|
1287 | <tt><A href="http://www.sgi.com/tech/stl/hash_map.html">hash_map</A></tt>,
|
---|
1288 | <A href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative Container</A>,
|
---|
1289 | <A href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed Associative Container</A>,
|
---|
1290 | <A href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair Associative Container</A>,
|
---|
1291 | <A href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique Hashed Associative Container</A>,
|
---|
1292 | <tt><A href="http://www.sgi.com/tech/stl/set.html">set</A></tt>,
|
---|
1293 | <tt><A href="http://www.sgi.com/tech/stl/Map.html">map</A></tt>
|
---|
1294 | <tt><A href="http://www.sgi.com/tech/stl/multiset.html">multiset</A></tt>,
|
---|
1295 | <tt><A href="http://www.sgi.com/tech/stl/Multimap.html">multimap</A></tt>,
|
---|
1296 | <tt><A href="http://www.sgi.com/tech/stl/hash_set.html">hash_set</A></tt>,
|
---|
1297 | <tt><A href="http://www.sgi.com/tech/stl/hash_multiset.html">hash_multiset</A></tt>,
|
---|
1298 | <tt><A href="http://www.sgi.com/tech/stl/hash_multimap.html">hash_multimap</A></tt>,
|
---|
1299 | <tt><A href="sparse_hash_set.html">sparse_hash_set</A></tt>,
|
---|
1300 | <tt><A href="sparse_hash_map.html">sparse_hash_map</A></tt>,
|
---|
1301 | <tt><A href="dense_hash_set.html">dense_hash_set</A></tt>
|
---|
1302 |
|
---|
1303 | </BODY>
|
---|
1304 | </HTML>
|
---|