Got an error on line 19: error : no 'operator (int)' declared for postfix ' ' [-fpermissive]

#include<bits/stdc  .h>
using namespace std;
class sample
{
    int x,y;
public:
    sample(){x=y=0;}
    void display()
    {
        cout<<endl<<"x="<<x<<" and y= "<<y;
    }
    void operator   (){x  ;y  ;}
};

int main()
{
    sample s1;
    sample s2;
    s1  ;
      s2;
      s1;
    s1.display();
    s2.display();
    return 0;
}

Error on code line:

s1  ;

CodePudding user response：

TURBO C ? Haven't heard that name in a LONG time. That is a compiler from an era before C was even standardized, and is not representative of C anymore.

Prefix increment and post-increment are different functions. You can't just overload one and expect both to work.

Also your signature is wrong. It should return a type matching the class it's called on. For example:

class sample
{
public:
...
    // prefix
    sample & operator   ()  {x  ; y  ; return *this; }

    // postfix (the int is a dummy just to differentiate the signature)
    sample operator   (int) {
        sample copy(*this); 
        x  ; y  ; 
        return copy;
    }
};

The value of the return type is the main difference between the two so it's pointless for your operator to return void. One returns a reference, since it represents the incremented object, while the postfix version returns a copy that is the state of the pre-incremented object.

CodePudding user response：

operator () is for overloading the prefix increment operator, you need to also add a postfix overload:

class sample
{
    int x, y;
public:
    // ...
    void operator  (){
        x  ;
        y  ;
    }
    void operator  (int) {
        operator  ();
    }
};