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 // Copyright (c) 2011 The Chromium Authors. All rights reserved.

 // Use of this source code is governed by a BSD-style license that can be

 // found in the LICENSE file.

 // Derived from google3/util/gtl/stl_util.h

 #ifndef BASE_STL_UTIL_H_

 #define BASE_STL_UTIL_H_

 #include <algorithm>

 #include <functional>

 #include <iterator>

 #include <string>

 #include <vector>

 #include "base/logging.h"

 // Clears internal memory of an STL object.

 // STL clear()/reserve(0) does not always free internal memory allocated

 // This function uses swap/destructor to ensure the internal memory is freed.

 template<class T>

 void STLClearObject(T* obj) {

   T tmp;

   tmp.swap(*obj);

   // Sometimes "T tmp" allocates objects with memory (arena implementation?).

   // Hence using additional reserve(0) even if it doesn't always work.

   obj->reserve(0);

 }

 // For a range within a container of pointers, calls delete (non-array version)

 // on these pointers.

 // NOTE: for these three functions, we could just implement a DeleteObject

 // functor and then call for_each() on the range and functor, but this

 // requires us to pull in all of algorithm.h, which seems expensive.

 // For hash_[multi]set, it is important that this deletes behind the iterator

 // because the hash_set may call the hash function on the iterator when it is

 // advanced, which could result in the hash function trying to deference a

 // stale pointer.

 template <class ForwardIterator>

 void STLDeleteContainerPointers(ForwardIterator begin, ForwardIterator end) {

   while (begin != end) {

     ForwardIterator temp = begin;

     ++begin;

     delete *temp;

   }

 }

 // For a range within a container of pairs, calls delete (non-array version) on

 // BOTH items in the pairs.

 // NOTE: Like STLDeleteContainerPointers, it is important that this deletes

 // behind the iterator because if both the key and value are deleted, the

 // container may call the hash function on the iterator when it is advanced,

 // which could result in the hash function trying to dereference a stale

 // pointer.

 template <class ForwardIterator>

 void STLDeleteContainerPairPointers(ForwardIterator begin,

                                     ForwardIterator end) {

   while (begin != end) {

     ForwardIterator temp = begin;

     ++begin;

     delete temp->first;

     delete temp->second;

   }

 }

 // For a range within a container of pairs, calls delete (non-array version) on

 // the FIRST item in the pairs.

 // NOTE: Like STLDeleteContainerPointers, deleting behind the iterator.

 template <class ForwardIterator>

 void STLDeleteContainerPairFirstPointers(ForwardIterator begin,

                                          ForwardIterator end) {

   while (begin != end) {

     ForwardIterator temp = begin;

     ++begin;

     delete temp->first;

   }

 }

 // For a range within a container of pairs, calls delete.

 // NOTE: Like STLDeleteContainerPointers, deleting behind the iterator.

 // Deleting the value does not always invalidate the iterator, but it may

 // do so if the key is a pointer into the value object.

 template <class ForwardIterator>

 void STLDeleteContainerPairSecondPointers(ForwardIterator begin,

                                           ForwardIterator end) {

   while (begin != end) {

     ForwardIterator temp = begin;

     ++begin;

     delete temp->second;

   }

 }

 // To treat a possibly-empty vector as an array, use these functions.

 // If you know the array will never be empty, you can use &*v.begin()

 // directly, but that is undefined behaviour if |v| is empty.

 template<typename T>

 inline T* vector_as_array(std::vector<T>* v) {

   return v->empty() ? NULL : &*v->begin();

 }

 template<typename T>

 inline const T* vector_as_array(const std::vector<T>* v) {

   return v->empty() ? NULL : &*v->begin();

 }

 // Return a mutable char* pointing to a string's internal buffer,

 // which may not be null-terminated. Writing through this pointer will

 // modify the string.

 //

 // string_as_array(&str)[i] is valid for 0 <= i < str.size() until the

 // next call to a string method that invalidates iterators.

 //

 // As of 2006-04, there is no standard-blessed way of getting a

 // mutable reference to a string's internal buffer. However, issue 530

 // (http://www.open-std.org/JTC1/SC22/WG21/docs/lwg-active.html#530)

 // proposes this as the method. According to Matt Austern, this should

 // already work on all current implementations.

 inline char* string_as_array(std::string* str) {

   // DO NOT USE const_cast<char*>(str->data())

   return str->empty() ? NULL : &*str->begin();

 }

 // The following functions are useful for cleaning up STL containers whose

 // elements point to allocated memory.

 // STLDeleteElements() deletes all the elements in an STL container and clears

 // the container.  This function is suitable for use with a vector, set,

 // hash_set, or any other STL container which defines sensible begin(), end(),

 // and clear() methods.

 //

 // If container is NULL, this function is a no-op.

 //

 // As an alternative to calling STLDeleteElements() directly, consider

 // STLElementDeleter (defined below), which ensures that your container's

 // elements are deleted when the STLElementDeleter goes out of scope.

 template <class T>

 void STLDeleteElements(T* container) {

   if (!container)

     return;

   STLDeleteContainerPointers(container->begin(), container->end());

   container->clear();

 }

 // Given an STL container consisting of (key, value) pairs, STLDeleteValues

 // deletes all the "value" components and clears the container.  Does nothing

 // in the case it's given a NULL pointer.

 template <class T>

 void STLDeleteValues(T* container) {

   if (!container)

     return;

   for (typename T::iterator i(container->begin()); i != container->end(); ++i)

     delete i->second;

   container->clear();

 }

 // The following classes provide a convenient way to delete all elements or

 // values from STL containers when they goes out of scope.  This greatly

 // simplifies code that creates temporary objects and has multiple return

 // statements.  Example:

 //

 // vector<MyProto *> tmp_proto;

 // STLElementDeleter<vector<MyProto *> > d(&tmp_proto);

 // if (...) return false;

 // ...

 // return success;

 // Given a pointer to an STL container this class will delete all the element

 // pointers when it goes out of scope.

 template<class T>

 class STLElementDeleter {

  public:

   STLElementDeleter<T>(T* container) : container_(container) {}

   ~STLElementDeleter<T>() { STLDeleteElements(container_); }

  private:

   T* container_;

 };

 // Given a pointer to an STL container this class will delete all the value

 // pointers when it goes out of scope.

 template<class T>

 class STLValueDeleter {

  public:

   STLValueDeleter<T>(T* container) : container_(container) {}

   ~STLValueDeleter<T>() { STLDeleteValues(container_); }

  private:

   T* container_;

 };

 // Test to see if a set, map, hash_set or hash_map contains a particular key.

 // Returns true if the key is in the collection.

 template <typename Collection, typename Key>

 bool ContainsKey(const Collection& collection, const Key& key) {

   return collection.find(key) != collection.end();

 }

 namespace base {

 // Returns true if the container is sorted.

 template <typename Container>

 bool STLIsSorted(const Container& cont) {

   return std::adjacent_find(cont.begin(), cont.end(),

                             std::greater<typename Container::value_type>())

       == cont.end();

 }

 // Returns a new ResultType containing the difference of two sorted containers.

 template <typename ResultType, typename Arg1, typename Arg2>

 ResultType STLSetDifference(const Arg1& a1, const Arg2& a2) {

   DCHECK(STLIsSorted(a1));

   DCHECK(STLIsSorted(a2));

   ResultType difference;

   std::set_difference(a1.begin(), a1.end(),

                       a2.begin(), a2.end(),

                       std::inserter(difference, difference.end()));

   return difference;

 }

 }  // namespace base

 #endif  // BASE_STL_UTIL_H_