[C/C++标准库]_[初级]_[函数对象functor的使用]

来源：互联网发布：vb中string是什么意思编辑：程序博客网时间：2024/05/16 00:52

Functor

std::set

场景:

1. functor其实就是一个类对象,因为它重载了operator()操作符,所以可以把实例当作函数名那样操作,在C里也只有函数可以这么做.比如语句 f(1,2);在cpp

必须通过上下文判断f是对象还是函数.

2.在使用stl的容器类或算法函数时，经常需要自己传入一个functo作为参数或模板.

#include <string.h>#include <iostream>#include <fstream>#include <string>#include <utility>#include <set>using namespace std;class Person{public:Person(int code,const string& name,const string& grade,const string& address):code_(code){name_ = name;grade_ = grade;address_ = address;}~Person(){}int code_;// 学号.string name_;// name.string grade_; //grade.string address_;void operator()(){cout << " code_: " << code_      << " name_: " << name_      << " grade_: " << grade_      << " address_: " << address_ << endl;}};class PersonCompare{public:bool operator() (const Person* p1, const Person* p2) const {return p1->code_ < p2->code_;}/* data */};class test_functor{public:void operator()(int x,int y){cout << "x+y: " << x+y << endl;}/* data */};int main(int argc, char const *argv[]){//1.simple functortest_functor tf;tf(1,2);//2.sort functortypedef set<Person*,PersonCompare> PersonSet;PersonSet::iterator it;PersonSet ps;ps.insert(new Person(3,"张三","高三(1)班","北京朝阳区"));ps.insert(new Person(2,"李四","高三(2)班","北京海淀区"));ps.insert(new Person(1,"龙五","高三(3)班","北京王府井"));// ps.insert(new Person(1,"龙四","高三(3)班","北京王府井"));for (it = ps.begin(); it != ps.end(); ++it){(*(*it))();}cout << endl;pair<PersonSet::iterator,bool> res = ps.insert(new Person(1,"张四","高三(3)班","北京王府井"));if (!res.second){cout << "insert fail,exist name: " << (*(res.first))->name_ << endl;}for (it = ps.begin(); it != ps.end(); ++it){(*(*it))();}return 0;}

输出:

x+y: 3 code_: 1 name_: 龙五 grade_: 高三(3)班 address_: 北京王府井 code_: 2 name_: 李四 grade_: 高三(2)班 address_: 北京海淀区 code_: 3 name_: 张三 grade_: 高三(1)班 address_: 北京朝阳区insert fail,exist name: 龙五 code_: 1 name_: 龙五 grade_: 高三(3)班 address_: 北京王府井 code_: 2 name_: 李四 grade_: 高三(2)班 address_: 北京海淀区 code_: 3 name_: 张三 grade_: 高三(1)班 address_: 北京朝阳区[Finished in 0.1s]

参考:

1.《C++ Standard Library, The: A Tutorial and Reference》

0 0