Chromium是一个伟大的、庞大的开源工程,很多值得我们学习的地方。
今天与大家分享的就是Chromium下base中的stl_util,是对stl的补充,封装,更有利于我们的使用,完全可以移植到自己的C++工程项目中来。
1 释放STL内存 Clears internal memory of an STL object.
我们知道,vector的clear()方法式清除了vector中的内容,但是vector object所占的内存不会清除。
因此,std_util中有个这个方法:
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);
}
也就是使用swap,之前写过一篇博客: 《实战c++中的vector系列–正确释放vector的内存(clear(), swap(), shrink_to_fit())》 地址:http://blog.csdn.net/wangshubo1989/article/details/50359750
2 释放容器内的指针对象 这里隐藏了一个巨大的坑儿,就是迭代器的失效问题,之前也有博客里面介绍过:
《实战c++中的vector系列–可怕的迭代器失效(vector重新申请内存)》 地址:http://blog.csdn.net/wangshubo1989/article/details/50334297
《实战c++中的vector系列–可怕的迭代器失效之二(删除vector中元素)》 地址:http://blog.csdn.net/wangshubo1989/article/details/50334503
template <class ForwardIterator>void STLDeleteContainerPointers(ForwardIterator begin, ForwardIterator end) { while (begin != end) {
ForwardIterator temp = begin;
++begin; delete *temp;
}
}
3 正确删除容器内pairs对象
template <class ForwardIterator>void STLDeleteContainerPairPointers(ForwardIterator begin,
ForwardIterator end) { while (begin != end) {
ForwardIterator temp = begin;
++begin; delete temp->first; delete temp->second;
}
}
4 删除容器内pairs对象中的第一个元素
template <class ForwardIterator>void STLDeleteContainerPairFirstPointers(ForwardIterator begin,
ForwardIterator end) { while (begin != end) {
ForwardIterator temp = begin;
++begin; delete temp->first;
}
}
5 删除容器内pairs对象中的第二个元素
template <class ForwardIterator>void STLDeleteContainerPairSecondPointers(ForwardIterator begin,
ForwardIterator end) { while (begin != end) {
ForwardIterator temp = begin;
++begin; delete temp->second;
}
}
6 vector转为数组 一定要注意,vector可能为空的情况下。
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();
}
7 string转为数组 还是是要注意string为空。
inline char* string_as_array(std::string* str) { // DO NOT USE const_cast<char*>(str->data())
return str->empty() ? NULL : &*str->begin();
}
8 查找关联容器中是否有某个特定的key 没什么好说的,提高效率,函数的参数为const引用类型。
template <typename Collection, typename Key>bool ContainsKey(const Collection& collection, const Key& key) { return collection.find(key) != collection.end();
}
9 判断容器是否有序 这里用到了adjacent_find,在一个数组中寻找两个相邻的元素;
template <typename Container>bool STLIsSorted(const Container& cont) { // Note: Use reverse iterator on container to ensure we only require
// value_type to implement operator<.
return std::adjacent_find(cont.rbegin(), cont.rend(), std::less<typename Container::value_type>())
== cont.rend();
}
10 获得两个有序容器的不同 这里用到了DCHECK,是自己定义的宏:
#define DCHECK(condition) \
LAZY_STREAM(LOG_STREAM(DCHECK), DCHECK_IS_ON ? !(condition) : false) \
<< "Check failed: " #condition ". "
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;
}
11 合并两个有序的容器
template <typename ResultType, typename Arg1, typename Arg2>
ResultType STLSetUnion(const Arg1& a1, const Arg2& a2) {
DCHECK(STLIsSorted(a1));
DCHECK(STLIsSorted(a2));
ResultType result; std::set_union(a1.begin(), a1.end(),
a2.begin(), a2.end(), std::inserter(result, result.end())); return result;
}
12 同时包含在两个容器中的元素 set_intersection:同时包含第一个和第二个集合中的元素
template <typename ResultType, typename Arg1, typename Arg2>
ResultType STLSetIntersection(const Arg1& a1, const Arg2& a2) {
DCHECK(STLIsSorted(a1));
DCHECK(STLIsSorted(a2));
ResultType result; std::set_intersection(a1.begin(), a1.end(),
a2.begin(), a2.end(), std::inserter(result, result.end())); return result;
}
13 判断一个容器是否包含另一个容器的所有内容
template <typename Arg1, typename Arg2>bool STLIncludes(const Arg1& a1, const Arg2& a2) {
DCHECK(STLIsSorted(a1));
DCHECK(STLIsSorted(a2)); return std::includes(a1.begin(), a1.end(),
a2.begin(), a2.end());
}
应用: 对上面介绍的方法进行简单的使用,看看吧:
#include<iostream>#include<vector>#include<algorithm>#include"stl_util.h"int main()
{ std::vector<int> numbers{1, 2, 3, 4, 6}; std::vector<int> numbers1{ 1, 2, 3 ,4}; std::cout << "Test STLIsSorted:{1, 2, 3, 4, 6}" << std::endl; std::cout << std::boolalpha <<STLIsSorted(numbers) << std::endl << std::endl; std::cout << "Test STLSetDifference {1, 2, 3, 4, 6} and { 1, 2, 3 ,4}:" << std::endl; std::vector<int> difference_result;
difference_result = STLSetDifference<std::vector<int>, std::vector<int>, std::vector<int>>(numbers, numbers1); for(auto iter: difference_result)
{ std::cout << iter << std::endl << std::endl;
} std::cout << "Test STLSetIntersection {1, 2, 3, 4, 6} and { 1, 2, 3 ,4}:" << std::endl; std::vector<int> intersection_result;
intersection_result = STLSetIntersection<std::vector<int>, std::vector<int>, std::vector<int>>(numbers, numbers1); for (auto iter : intersection_result)
{ std::cout << iter << " " ;
} std::cout << std::endl; std::cout << "Test STLIncludes {1, 2, 3, 4, 6} and { 1, 2, 3 ,4}:" << std::endl; std::cout << std::boolalpha << STLIncludes(numbers, numbers1) << std::endl << std::endl; std::cout << "Test STLClearObject:" << std::endl;
STLClearObject(&numbers); std::cout << "vector size:" << numbers.size() << std::endl; std::cout << "vector capacity:" << numbers.capacity() << std::endl << std::endl;
system("pause"); return 0;
}
输出结果:
Test STLIsSorted:{1, 2, 3, 4, 6}trueTest STLSetDifference {1, 2, 3, 4, 6} and { 1, 2, 3 ,4}:6Test STLSetIntersection {1, 2, 3, 4, 6} and { 1, 2, 3 ,4}:1 2 3 4Test STLIncludes {1, 2, 3, 4, 6} and { 1, 2, 3 ,4}:trueTest STLClearObject:vector size:0vector capacity:0