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1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. |
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2 // Use of this source code is governed by a BSD-style license that can be |
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3 // found in the LICENSE file. |
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4 |
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5 // Derived from google3/util/gtl/stl_util.h |
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6 |
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7 #ifndef BASE_STL_UTIL_H_ |
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8 #define BASE_STL_UTIL_H_ |
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9 |
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10 #include <algorithm> |
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11 #include <functional> |
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12 #include <iterator> |
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13 #include <string> |
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14 #include <vector> |
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15 |
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16 #include "base/logging.h" |
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17 |
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18 // Clears internal memory of an STL object. |
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19 // STL clear()/reserve(0) does not always free internal memory allocated |
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20 // This function uses swap/destructor to ensure the internal memory is freed. |
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21 template<class T> |
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22 void STLClearObject(T* obj) { |
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23 T tmp; |
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24 tmp.swap(*obj); |
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25 // Sometimes "T tmp" allocates objects with memory (arena implementation?). |
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26 // Hence using additional reserve(0) even if it doesn't always work. |
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27 obj->reserve(0); |
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28 } |
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29 |
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30 // For a range within a container of pointers, calls delete (non-array version) |
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31 // on these pointers. |
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32 // NOTE: for these three functions, we could just implement a DeleteObject |
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33 // functor and then call for_each() on the range and functor, but this |
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34 // requires us to pull in all of algorithm.h, which seems expensive. |
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35 // For hash_[multi]set, it is important that this deletes behind the iterator |
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36 // because the hash_set may call the hash function on the iterator when it is |
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37 // advanced, which could result in the hash function trying to deference a |
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38 // stale pointer. |
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39 template <class ForwardIterator> |
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40 void STLDeleteContainerPointers(ForwardIterator begin, ForwardIterator end) { |
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41 while (begin != end) { |
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42 ForwardIterator temp = begin; |
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43 ++begin; |
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44 delete *temp; |
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45 } |
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46 } |
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47 |
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48 // For a range within a container of pairs, calls delete (non-array version) on |
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49 // BOTH items in the pairs. |
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50 // NOTE: Like STLDeleteContainerPointers, it is important that this deletes |
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51 // behind the iterator because if both the key and value are deleted, the |
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52 // container may call the hash function on the iterator when it is advanced, |
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53 // which could result in the hash function trying to dereference a stale |
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54 // pointer. |
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55 template <class ForwardIterator> |
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56 void STLDeleteContainerPairPointers(ForwardIterator begin, |
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57 ForwardIterator end) { |
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58 while (begin != end) { |
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59 ForwardIterator temp = begin; |
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60 ++begin; |
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61 delete temp->first; |
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62 delete temp->second; |
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63 } |
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64 } |
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65 |
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66 // For a range within a container of pairs, calls delete (non-array version) on |
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67 // the FIRST item in the pairs. |
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68 // NOTE: Like STLDeleteContainerPointers, deleting behind the iterator. |
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69 template <class ForwardIterator> |
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70 void STLDeleteContainerPairFirstPointers(ForwardIterator begin, |
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71 ForwardIterator end) { |
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72 while (begin != end) { |
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73 ForwardIterator temp = begin; |
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74 ++begin; |
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75 delete temp->first; |
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76 } |
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77 } |
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78 |
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79 // For a range within a container of pairs, calls delete. |
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80 // NOTE: Like STLDeleteContainerPointers, deleting behind the iterator. |
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81 // Deleting the value does not always invalidate the iterator, but it may |
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82 // do so if the key is a pointer into the value object. |
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83 template <class ForwardIterator> |
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84 void STLDeleteContainerPairSecondPointers(ForwardIterator begin, |
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85 ForwardIterator end) { |
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86 while (begin != end) { |
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87 ForwardIterator temp = begin; |
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88 ++begin; |
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89 delete temp->second; |
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90 } |
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91 } |
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92 |
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93 // To treat a possibly-empty vector as an array, use these functions. |
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94 // If you know the array will never be empty, you can use &*v.begin() |
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95 // directly, but that is undefined behaviour if |v| is empty. |
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96 template<typename T> |
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97 inline T* vector_as_array(std::vector<T>* v) { |
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98 return v->empty() ? NULL : &*v->begin(); |
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99 } |
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100 |
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101 template<typename T> |
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102 inline const T* vector_as_array(const std::vector<T>* v) { |
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103 return v->empty() ? NULL : &*v->begin(); |
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104 } |
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105 |
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106 // Return a mutable char* pointing to a string's internal buffer, |
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107 // which may not be null-terminated. Writing through this pointer will |
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108 // modify the string. |
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109 // |
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110 // string_as_array(&str)[i] is valid for 0 <= i < str.size() until the |
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111 // next call to a string method that invalidates iterators. |
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112 // |
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113 // As of 2006-04, there is no standard-blessed way of getting a |
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114 // mutable reference to a string's internal buffer. However, issue 530 |
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115 // (http://www.open-std.org/JTC1/SC22/WG21/docs/lwg-active.html#530) |
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116 // proposes this as the method. According to Matt Austern, this should |
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117 // already work on all current implementations. |
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118 inline char* string_as_array(std::string* str) { |
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119 // DO NOT USE const_cast<char*>(str->data()) |
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120 return str->empty() ? NULL : &*str->begin(); |
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121 } |
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122 |
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123 // The following functions are useful for cleaning up STL containers whose |
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124 // elements point to allocated memory. |
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125 |
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126 // STLDeleteElements() deletes all the elements in an STL container and clears |
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127 // the container. This function is suitable for use with a vector, set, |
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128 // hash_set, or any other STL container which defines sensible begin(), end(), |
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129 // and clear() methods. |
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130 // |
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131 // If container is NULL, this function is a no-op. |
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132 // |
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133 // As an alternative to calling STLDeleteElements() directly, consider |
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134 // STLElementDeleter (defined below), which ensures that your container's |
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135 // elements are deleted when the STLElementDeleter goes out of scope. |
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136 template <class T> |
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137 void STLDeleteElements(T* container) { |
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138 if (!container) |
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139 return; |
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140 STLDeleteContainerPointers(container->begin(), container->end()); |
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141 container->clear(); |
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142 } |
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143 |
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144 // Given an STL container consisting of (key, value) pairs, STLDeleteValues |
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145 // deletes all the "value" components and clears the container. Does nothing |
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146 // in the case it's given a NULL pointer. |
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147 template <class T> |
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148 void STLDeleteValues(T* container) { |
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149 if (!container) |
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150 return; |
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151 for (typename T::iterator i(container->begin()); i != container->end(); ++i) |
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152 delete i->second; |
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153 container->clear(); |
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154 } |
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155 |
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156 |
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157 // The following classes provide a convenient way to delete all elements or |
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158 // values from STL containers when they goes out of scope. This greatly |
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159 // simplifies code that creates temporary objects and has multiple return |
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160 // statements. Example: |
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161 // |
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162 // vector<MyProto *> tmp_proto; |
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163 // STLElementDeleter<vector<MyProto *> > d(&tmp_proto); |
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164 // if (...) return false; |
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165 // ... |
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166 // return success; |
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167 |
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168 // Given a pointer to an STL container this class will delete all the element |
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169 // pointers when it goes out of scope. |
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170 template<class T> |
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171 class STLElementDeleter { |
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172 public: |
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173 STLElementDeleter<T>(T* container) : container_(container) {} |
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174 ~STLElementDeleter<T>() { STLDeleteElements(container_); } |
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175 |
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176 private: |
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177 T* container_; |
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178 }; |
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179 |
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180 // Given a pointer to an STL container this class will delete all the value |
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181 // pointers when it goes out of scope. |
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182 template<class T> |
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183 class STLValueDeleter { |
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184 public: |
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185 STLValueDeleter<T>(T* container) : container_(container) {} |
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186 ~STLValueDeleter<T>() { STLDeleteValues(container_); } |
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187 |
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188 private: |
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189 T* container_; |
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190 }; |
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191 |
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192 // Test to see if a set, map, hash_set or hash_map contains a particular key. |
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193 // Returns true if the key is in the collection. |
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194 template <typename Collection, typename Key> |
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195 bool ContainsKey(const Collection& collection, const Key& key) { |
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196 return collection.find(key) != collection.end(); |
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197 } |
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198 |
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199 namespace base { |
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200 |
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201 // Returns true if the container is sorted. |
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202 template <typename Container> |
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203 bool STLIsSorted(const Container& cont) { |
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204 return std::adjacent_find(cont.begin(), cont.end(), |
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205 std::greater<typename Container::value_type>()) |
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206 == cont.end(); |
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207 } |
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208 |
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209 // Returns a new ResultType containing the difference of two sorted containers. |
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210 template <typename ResultType, typename Arg1, typename Arg2> |
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211 ResultType STLSetDifference(const Arg1& a1, const Arg2& a2) { |
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212 DCHECK(STLIsSorted(a1)); |
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213 DCHECK(STLIsSorted(a2)); |
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214 ResultType difference; |
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215 std::set_difference(a1.begin(), a1.end(), |
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216 a2.begin(), a2.end(), |
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217 std::inserter(difference, difference.end())); |
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218 return difference; |
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219 } |
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220 |
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221 } // namespace base |
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222 |
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223 #endif // BASE_STL_UTIL_H_ |