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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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// Derived from google3/util/gtl/stl_util.h
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#ifndef BASE_STL_UTIL_H_
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#define BASE_STL_UTIL_H_
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#include "base/logging.h"
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// Clears internal memory of an STL object.
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// STL clear()/reserve(0) does not always free internal memory allocated
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// This function uses swap/destructor to ensure the internal memory is freed.
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void STLClearObject(T* obj) {
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// Sometimes "T tmp" allocates objects with memory (arena implementation?).
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// Hence using additional reserve(0) even if it doesn't always work.
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// For a range within a container of pointers, calls delete (non-array version)
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// NOTE: for these three functions, we could just implement a DeleteObject
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// functor and then call for_each() on the range and functor, but this
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// requires us to pull in all of algorithm.h, which seems expensive.
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// For hash_[multi]set, it is important that this deletes behind the iterator
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// because the hash_set may call the hash function on the iterator when it is
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// advanced, which could result in the hash function trying to deference a
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template <class ForwardIterator>
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void STLDeleteContainerPointers(ForwardIterator begin, ForwardIterator end) {
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while (begin != end) {
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ForwardIterator temp = begin;
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// For a range within a container of pairs, calls delete (non-array version) on
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// BOTH items in the pairs.
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// NOTE: Like STLDeleteContainerPointers, it is important that this deletes
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// behind the iterator because if both the key and value are deleted, the
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// container may call the hash function on the iterator when it is advanced,
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// which could result in the hash function trying to dereference a stale
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template <class ForwardIterator>
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void STLDeleteContainerPairPointers(ForwardIterator begin,
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ForwardIterator end) {
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while (begin != end) {
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ForwardIterator temp = begin;
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// For a range within a container of pairs, calls delete (non-array version) on
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// the FIRST item in the pairs.
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// NOTE: Like STLDeleteContainerPointers, deleting behind the iterator.
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template <class ForwardIterator>
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void STLDeleteContainerPairFirstPointers(ForwardIterator begin,
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ForwardIterator end) {
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while (begin != end) {
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ForwardIterator temp = begin;
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// For a range within a container of pairs, calls delete.
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// NOTE: Like STLDeleteContainerPointers, deleting behind the iterator.
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// Deleting the value does not always invalidate the iterator, but it may
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// do so if the key is a pointer into the value object.
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template <class ForwardIterator>
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void STLDeleteContainerPairSecondPointers(ForwardIterator begin,
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ForwardIterator end) {
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while (begin != end) {
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ForwardIterator temp = begin;
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// To treat a possibly-empty vector as an array, use these functions.
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// If you know the array will never be empty, you can use &*v.begin()
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// directly, but that is undefined behaviour if |v| is empty.
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inline T* vector_as_array(std::vector<T>* v) {
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return v->empty() ? NULL : &*v->begin();
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inline const T* vector_as_array(const std::vector<T>* v) {
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return v->empty() ? NULL : &*v->begin();
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// Return a mutable char* pointing to a string's internal buffer,
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// which may not be null-terminated. Writing through this pointer will
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// modify the string.
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// string_as_array(&str)[i] is valid for 0 <= i < str.size() until the
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// next call to a string method that invalidates iterators.
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// As of 2006-04, there is no standard-blessed way of getting a
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// mutable reference to a string's internal buffer. However, issue 530
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// (http://www.open-std.org/JTC1/SC22/WG21/docs/lwg-active.html#530)
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// proposes this as the method. According to Matt Austern, this should
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// already work on all current implementations.
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inline char* string_as_array(std::string* str) {
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// DO NOT USE const_cast<char*>(str->data())
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return str->empty() ? NULL : &*str->begin();
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// The following functions are useful for cleaning up STL containers whose
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// elements point to allocated memory.
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// STLDeleteElements() deletes all the elements in an STL container and clears
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// the container. This function is suitable for use with a vector, set,
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// hash_set, or any other STL container which defines sensible begin(), end(),
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// and clear() methods.
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// If container is NULL, this function is a no-op.
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// As an alternative to calling STLDeleteElements() directly, consider
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// STLElementDeleter (defined below), which ensures that your container's
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// elements are deleted when the STLElementDeleter goes out of scope.
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void STLDeleteElements(T* container) {
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STLDeleteContainerPointers(container->begin(), container->end());
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// Given an STL container consisting of (key, value) pairs, STLDeleteValues
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// deletes all the "value" components and clears the container. Does nothing
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// in the case it's given a NULL pointer.
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void STLDeleteValues(T* container) {
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for (typename T::iterator i(container->begin()); i != container->end(); ++i)
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// The following classes provide a convenient way to delete all elements or
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// values from STL containers when they goes out of scope. This greatly
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// simplifies code that creates temporary objects and has multiple return
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// statements. Example:
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// vector<MyProto *> tmp_proto;
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// STLElementDeleter<vector<MyProto *> > d(&tmp_proto);
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// if (...) return false;
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// Given a pointer to an STL container this class will delete all the element
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// pointers when it goes out of scope.
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class STLElementDeleter {
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STLElementDeleter<T>(T* container) : container_(container) {}
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~STLElementDeleter<T>() { STLDeleteElements(container_); }
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// Given a pointer to an STL container this class will delete all the value
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// pointers when it goes out of scope.
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class STLValueDeleter {
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STLValueDeleter<T>(T* container) : container_(container) {}
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~STLValueDeleter<T>() { STLDeleteValues(container_); }
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// Test to see if a set, map, hash_set or hash_map contains a particular key.
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// Returns true if the key is in the collection.
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template <typename Collection, typename Key>
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bool ContainsKey(const Collection& collection, const Key& key) {
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return collection.find(key) != collection.end();
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// Returns true if the container is sorted.
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template <typename Container>
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bool STLIsSorted(const Container& cont) {
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// Note: Use reverse iterator on container to ensure we only require
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// value_type to implement operator<.
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return std::adjacent_find(cont.rbegin(), cont.rend(),
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std::less<typename Container::value_type>())
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// Returns a new ResultType containing the difference of two sorted containers.
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template <typename ResultType, typename Arg1, typename Arg2>
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ResultType STLSetDifference(const Arg1& a1, const Arg2& a2) {
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DCHECK(STLIsSorted(a1));
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DCHECK(STLIsSorted(a2));
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ResultType difference;
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std::set_difference(a1.begin(), a1.end(),
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a2.begin(), a2.end(),
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std::inserter(difference, difference.end()));
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// Returns a new ResultType containing the union of two sorted containers.
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template <typename ResultType, typename Arg1, typename Arg2>
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ResultType STLSetUnion(const Arg1& a1, const Arg2& a2) {
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DCHECK(STLIsSorted(a1));
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DCHECK(STLIsSorted(a2));
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std::set_union(a1.begin(), a1.end(),
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a2.begin(), a2.end(),
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std::inserter(result, result.end()));
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// Returns a new ResultType containing the intersection of two sorted
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template <typename ResultType, typename Arg1, typename Arg2>
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ResultType STLSetIntersection(const Arg1& a1, const Arg2& a2) {
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DCHECK(STLIsSorted(a1));
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DCHECK(STLIsSorted(a2));
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std::set_intersection(a1.begin(), a1.end(),
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a2.begin(), a2.end(),
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std::inserter(result, result.end()));
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// Returns true if the sorted container |a1| contains all elements of the sorted
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template <typename Arg1, typename Arg2>
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bool STLIncludes(const Arg1& a1, const Arg2& a2) {
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DCHECK(STLIsSorted(a1));
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DCHECK(STLIsSorted(a2));
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return std::includes(a1.begin(), a1.end(),
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a2.begin(), a2.end());
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#endif // BASE_STL_UTIL_H_