C++定义比较函数的几种方法-白红宇

C++定义比较函数的几种方法

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发布时间：2019-06-09

本文共 1730 字，大约阅读时间需要 5 分钟。

为了说明C++定义比较函数的几种方法，下面将以sort函数为例进行说明。

1.默认的内置比较函数，将按照对象内定义的<运算符由小到大排序

#include 
    
     #include 
     
      #include 
      
       #include 
       
        #include 
        
         using namespace std;int main(){    vector
         
           vec{"Hello", "World!", "Zhang San", "Li Si", "C++", "C"}; sort(vec.begin(), vec.end()); copy(vec.begin(), vec.end(), ostream_iterator
          
           (cout, "\n")); return 0;}

2.使用自定义的比较函数cmp，将按照从大到小的顺序排序

bool cmp(const string & a, const string & b){    return a > b;}int main(){    vector
    
      vec{"Hello", "World!", "Zhang San", "Li Si", "C++", "C"};    sort(vec.begin(), vec.end(), cmp);    copy(vec.begin(), vec.end(), ostream_iterator
     
      (cout, "\n"));    return 0;}

3.使用C++内置的Function object

int main(){    vector
    
      vec{"Hello", "World!", "Zhang San", "Li Si", "C++", "C"};    sort(vec.begin(), vec.end(), greater
     
      ());    copy(vec.begin(), vec.end(), ostream_iterator
      
       (cout, "\n"));    return 0;}

4.使用C++11新支持的lambda表达式

int main(){    vector
    
      vec{"Hello", "World!", "Zhang San", "Li Si", "C++", "C"};    sort(vec.begin(), vec.end(), [](const string & a, const string & b) {return a > b;});    copy(vec.begin(), vec.end(), ostream_iterator
     
      (cout, "\n"));    return 0;}

5.重载()运算符，即自定义一个Function object

class cmp{public:    bool operator () (const string & a, const string & b) {        return a > b;    }};int main(){    vector
    
      vec{"Hello", "World!", "Zhang San", "Li Si", "C++", "C"};    sort(vec.begin(), vec.end(), cmp());    copy(vec.begin(), vec.end(), ostream_iterator
     
      (cout, "\n"));    return 0;}