stl 常用遍歷算法(for_each transform)
示例代碼(結(jié)論在結(jié)尾!!!!)
#include<IOStream>
using namespace std;
#include"vector"
#include"map"
#include"string"
#include"list"
#include"set"
#include"functional"
#include"iterator"//輸出流迭代器
void printV(vector<int> &v)
{
for (vector<int>::iterator it = v.begin(); it != v.end(); it++);//用迭代器的方式打印出來
{
cout << *it << endl;
}
}
void printList(list<int> &v)
{
for (list<int>::iterator it = v.begin(); it != v.end(); it++);//用迭代器的方式打印出來
{
cout << *it << endl;
}
}
void showElem(int &n)
{
cout << n << " ";
}
class CMyShow
{
public:
CMyShow()
{
num = 0;
}
void operator()(int &n)
{
num++;
cout << n << " ";
}
void printNum()
{
cout << "num:" << num << endl;
}
protected:
private:
int num;
};
void main11_foreach()
{
vector<int> v1;
v1.push_back(1);
v1.push_back(3);
v1.push_back(5);
printV(v1);
cout << endl;
//函數(shù)對(duì)象 回調(diào)函數(shù)入口
for_each(v1.begin(), v1.end(), showElem);
cout << endl;
for_each(v1.begin(), v1.end(), CMyShow());
cout << endl;
CMyShow mya;
CMyShow my1=for_each(v1.begin(), v1.end(), mya);//初始化
my1.printNum();//打印出來了調(diào)用次數(shù)
mya.printNum();//mya my1是二個(gè)不同的對(duì)象
my1 = for_each(v1.begin(), v1.end(), mya);//給my1賦值
my1.printNum();
}
int increase(int i)
{
return i + 100;
}
void main22_transform()
{
vector<int> v1;
v1.push_back(1);
v1.push_back(3);
v1.push_back(5);
printV(v1);
cout << endl;
//使用回調(diào)函數(shù)
transform(v1.begin(), v1.end(), v1.begin(), increase);
printV(v1);
cout << endl;
//使用預(yù)定義的函數(shù)對(duì)象
transform(v1.begin(), v1.end(), v1.begin(), negate<int>());
printV(v1);
cout << endl;
//transform使用函數(shù)適配器
list<int> mylist;
mylist.resize(v1.size());
transform(v1.begin(), v1.end(), mylist.begin(), bind2nd(multiplies<int>(), 10));//第一個(gè)參數(shù)來著容器,第2個(gè)參數(shù)來自10
printList(mylist);
cout << endl;
//也可以把原酸結(jié)果直接輸出到屏幕
transform(v1.begin(), v1.end(), ostream_iterator<int>(cout, " "), negate<int>());
cout << endl;
}
void main33_foreach_pk_transform()
{
vector<int> v1;
v1.push_back(1);
v1.push_back(3);
v1.push_back(5);
vector<int> v2;
for_each(v1.begin(), v1.end(), showElem);
transform(v2.begin(), v2.end(), v2.begin(), showElem);
}
void main()
{
main33_foreach_pk_transform();
main22_transform();
main11_foreach();
cout << "hello..." << endl;
system("pause");
return;
}
結(jié)論:
for_each:用指定函數(shù)依此對(duì)指定范圍內(nèi)所有元素進(jìn)行迭代訪問，該函數(shù)不得修改序列中的元素(修改性算法)
一般情況下,使用的函數(shù)對(duì)象,參數(shù)是引用,沒有返回值 速度快
transform:與for_each類似,遍歷所有元素 但可對(duì)容器的元素進(jìn)行修改
參數(shù)一般不使用引用,而是還有返回值. 速度慢
