for_each
用于逐个遍历容器元素，它对迭代器区间[first，last)所指的每一个元素，执行由单参数函数对象f所定义的操作。方法返回函数对象。
函数的定义:
template<class _InIt,
class _Fn1> inline
_Fn1 for_each(_InIt _First, _InIt _Last, _Fn1 _Func)
{ // perform function for each element
_DEBUG_RANGE_PTR(_First, _Last, _Func);
_For_each_unchecked(_Unchecked(_First), _Unchecked(_Last), _Func);
return (_Func);
}
示例：
#include "stdafx.h"
#include "algorithm"
#include "iostream";
using namespace std;
#include "vector";
//函数对象
struct PrintV {
private:
int count;
public:
void operator()( int & value) {
count++;
value++;
cout << value << " ";
}
void print() {
cout << "调用次数 " << count << endl;
}
};
void print(vector<int> v) {
for (vector<int>::iterator it = v.begin(); it != v.end(); it++) {
cout << *it << " ";
}
}
int main()
{
vector<int> v;
v.push_back(1);
v.push_back(3);
v.push_back(2);
v.push_back(5);
v.push_back(4);
print(v);
cout << endl;
PrintV pv=for_each(v.begin(), v.end(), PrintV());
cout << endl;
pv.print();
print(v);
return 0;
}
for_each
transform
函数定义
template<class _InIt,
class _OutIt,
class _Fn1> inline
_OutIt transform(_InIt _First, _InIt _Last,
_OutIt _Dest, _Fn1 _Func)
{ // transform [_First, _Last) with _Func
_DEPRECATE_UNCHECKED(transform, _Dest);
return (_Transform_no_deprecate(_First, _Last, _Dest, _Func));
}
#if _ITERATOR_DEBUG_ARRAY_OVERLOADS
template<class _InIt,
class _OutTy,
size_t _OutSize,
class _Fn1> inline
_OutTy *transform(_InIt _First, _InIt _Last,
_OutTy (&_Dest)[_OutSize], _Fn1 _Func)
{ // transform [_First, _Last) with _Func, array dest
return (_Unchecked(
_Transform_no_deprecate(_First, _Last,
_Array_iterator<_OutTy, _OutSize>(_Dest), _Func)));
}
#endif /* _ITERATOR_DEBUG_ARRAY_OVERLOADS */
有两个重载函数，一个可以传入一元谓词，一个可以传入二元谓词。
与for_each区别
- for_each的仿函数可以返回void。transform的仿函数必须返回值。
- for_each的仿函数的参数是传入的引用。transform的仿函数的参数最好是值传递
示例
struct TranFunc2 {
private:
int count;
public:
int operator()(const int & left,const int & right) {
count++;
cout << "left right " << left << " " << right << endl;
return left+right;
}
void print() {
cout << "调用次数 " << count << endl;
}
};
void print(vector<int> v) {
for (vector<int>::iterator it = v.begin(); it != v.end(); it++) {
cout << *it << " ";
}
cout << endl;
}
int main()
{
vector<int> v;
v.push_back(1);
v.push_back(3);
v.push_back(2);
v.push_back(5);
v.push_back(4);
vector<int> v1=v;
v1.push_back(100);
cout << "遍历v" << endl;
print(v);
cout << "遍历v1" << endl;
print(v1);
vector<int>::iterator it=transform(v.begin(), v.end(), v1.begin(), TranFunc());
//v1的元素比v多一个所以，当执行transform后，v
//的迭代器到了末尾，而v1并没有
cout << "it==v1.end():" << (it==v1.end()) << endl;
print(v1);
//遍历v从begin到end。同时从v1的begin开始。最后
//结果存入到v中，从v的begin开始，结果返回v的迭代器
it=transform(v.begin(), v.end(), v1.begin(), v.begin(), TranFunc2());
//返回v的迭代器，v的迭代器已到末尾。
cout << "it==v1.end():" << (it == v.end()) << endl;
print(v);
return 0;
}
结果
transform.png
