Add std::pair with + operator

问题

Is there a simple way to make a+b work in the following example:

#include <utility>
#include <iostream>

int main ()
{
    std::pair<int, int> a=std::make_pair(1,2);
    std::pair<int, int> b=std::make_pair(3,3);
    std::pair<int, int> c = a+b;

    return 0;
}

回答1:

template <typename T,typename U>                                                   
std::pair<T,U> operator+(const std::pair<T,U> & l,const std::pair<T,U> & r) {   
    return {l.first+r.first,l.second+r.second};                                    
}                                                                                  
int main ()                                                                        
{                                                                                  
    std::pair<int, int> a=std::make_pair(1,2);                                     
    std::pair<int, int> b=std::make_pair(3,3);                                     
    std::pair<int, int> c = a+b;                                                   

    return 0;                                                                      
}

You can also do this with more template types to support adding two different types. Right now it supports adding pairs where the first and second are different types, but the two pairs and the return must have the same type.

If you want to make the function really versatile you could do this

template <typename T,typename U, typename V,typename W>                            
auto operator+(const std::pair<T,U> & l,const std::pair<V,W> & r)                  
-> std::pair<decltype(l.first+r.first),decltype(l.second+r.second)>                
{                                                                                  
    return {l.first+r.first,l.second+r.second};                                    
}

In c++14 you might be able to get away with auto instead of the trailing return type, if you explicitly return a pair.

回答2:

You can define an override for the binary + operator, specialized for pair<int, int> parameters:

std::pair<int, int> operator +(const std::pair<int, int>& x, const std::pair<int, int>& y) {
    return std::make_pair(x.first + y.first, x.second + y.second);
}

回答3:

Try this code :

#include <utility>
#include <iostream>
namespace
{
    std::pair<int,int> operator+(const std::pair<int,int> &a ,const  std::pair<int,int> &b )
    {
        return std::make_pair(a.first+b.first,a.second+b.second);
    }
}

int main ()
{
    std::pair<int, int> a=std::make_pair(1,2);
    std::pair<int, int> b=std::make_pair(3,3);
    std::pair<int, int> c = a+b;

    std::cout<<c.first<<"  "<<c.second;

    return 0;
}

回答4:

yes, you can overload the operator+ like this:

#include <utility>
#include <iostream>

std::pair<int,int> operator+(const std::pair<int, int>& x, const std::pair<int, int>& y) {
    return std::make_pair(x.first+y.first, x.second+y.second);
}

int main ()
{
    std::pair<int, int> a=std::make_pair(1,2);
    std::pair<int, int> b=std::make_pair(3,3);
    std::pair<int, int> c = a+b;

    std::cout << "c= ("<<c.first<<", "<<c.second<<")"<<std::endl;

    return 0;
}

will give you this:

./a.out 
c= (4, 5)

来源：https://stackoverflow.com/questions/21956119/add-stdpair-with-operator

标签

c++

stl