函数对象



//============================================================================
// Name        : JNIC++.cpp
// Author      : kris.zhang
// Version     :
// Copyright   : @[email protected]
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
/*
 * 定义了调用操作符的类，其对象常称为函数对象，即它们是行为类似函数的对象。
 */
struct absInt{
 absInt(size_t val=0):bound(val){}
 bool operator()(const string &s){
  return s.size()>=bound;
 }
 int operator() (int val){
  return 11;
 }
 int operator() (int val,int b){
   return val;
 }
private:
 std::string::size_type bound;
};

int main() {
 int i=-42;
 absInt absObj;
 vector<string> words;
 string next_word="s";
 words.push_back(next_word);
 words.push_back("dqwer");
 words.push_back("jfghghjh");
 words.push_back("fe");
 words.push_back("mfg");
 words.push_back("hsdf");
 unsigned int a=absObj(i);
  int b=absObj(i,i);
 cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!
 cout << "a="<<a<< endl; // prints !!!Hello World!!!
 cout << "b="<<b<< endl;
 for(int i=1;i<=10;i++){///使用函数对象计算长度在 1 到 10 个字符的单词数
  cout<<count_if(words.begin(),words.end(),absInt(i))<<"words"<< i<<" charactoers or longer!"<<endl;
 }

 return 0;
}

output：

a=11
b=-42
6words1 charactoers or longer!
5words2 charactoers or longer!
4words3 charactoers or longer!
3words4 charactoers or longer!
2words5 charactoers or longer!
1words6 charactoers or longer!