CODEWITHSUNDEEP
c++operator-overloadingoverloading
Traxys
Traxys

Reputation: 95

Overloading == compiling error c++

I made a simple struct named coord to hold , well coordinates , and I wanted to check if two coords were equal , so I looked how to do a proper operator overloading in another thread and came up with this :

#include <iostream>
using namespace std;

struct coord{
    int x;
    int y;

    inline bool operator==(const coord& lhs, const coord& rhs){
        if(lhs.x == rhs.x && lhs.y == rhs.y){
            return true;
        }
        else{
            return false;
        }
    }
};

int main(){
    coord a,b;
    a.x=5;
    a.y=5;
    b.x=a.x;
    b.y=a.y;
    if(a==b){
        cout<<"Working"<<endl;
    }
    return 0;
}

But at compiling I get a massive error who looks like :

g++ -c -o obj/main.o main.cpp -I../include
main.cpp:8:62: error: ‘bool coord::operator==(const coord&, const coord&)’ must take exactly one argument
     inline bool operator==(const coord& lhs, const coord& rhs){
                                                          ^
main.cpp: In function ‘int main()’:
main.cpp:24:6: error: no match for ‘operator==’ (operand types are ‘coord’ and ‘coord’)
  if(a==b){
      ^
main.cpp:24:6: note: candidates are:
In file included from /usr/include/c++/4.9.2/iosfwd:40:0,
             from /usr/include/c++/4.9.2/ios:38,
             from /usr/include/c++/4.9.2/ostream:38,
             from /usr/include/c++/4.9.2/iostream:39,
             from main.cpp:1:
/usr/include/c++/4.9.2/bits/postypes.h:216:5: note: template<class _StateT> bool std::operator==(const std::fpos<_StateT>&, const std::fpos<_StateT>&)
     operator==(const fpos<_SenttateT>& __lhs, const fpos<_StateT>& __rhs)
     ^

This goes on for a variety of other std things as ‘coord’ is not derived from ‘const std::basic_string<_CharT, _Traits, _Alloc>’ or ‘const std::allocator<_CharT>’ , the whole error being to long here it is on pastebin.

I hope someone understands whats going wrong here and can explain it to me

Upvotes: 0

Views: 93

Answers (1)

R Sahu
R Sahu

Reputation: 206737

There are couple of choices to get around the problem:

Member function

inline bool operator==(const coord& rhs) const {
    return (this->x == rhs.x && this->y == rhs.y);
}

When you use 

if(a==b){

the function is called on the object a and the argument to the function is b.

Non-member function

This can be defined outside the definition of struct coord.

struct coord{
    int x;
    int y;
};

bool operator==(const coord& lhs, const coord& rhs){
   return (lhs.x == rhs.x && lhs.y == rhs.y);
}

When you use 

if(a==b){

the function is called with a for lhs and b for rhs.

Upvotes: 5

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