Overriding function from caller source file in C++

Question

There is a c++ file called main.cpp.

main.cpp

#include "addition.h"
#include <iostream>
int main(){
   int x=2;
   int y=3;
   std::cout<<getsum(x,y);
}

This file includes custom header file called addition.h

addition.h

#include "my_adders.h"
namespace{
int getsum(int a,int b){
    return calculate_addition_h(a,b);
}
}

my_adders.h

#include <maths.h>
int calculate_addition_h(int p, int q){

      int sum=0;
      //Fn definitions
      return sum;
}

In main.cpp, i need to override the definition of calculate_addition_h function.

Is it possible?

I tried copying calculate_addition_h definition as well as declaration in main.cpp. However, when, i printed the o/p, calculate_addition_h method in my_adders.h was invoked, not the one in main.cpp.

Please note: I cannot make any changes to addition.h or my_adders.h.

Any help is appreciated!

I guess you could put your own version in a separate namespace (e.g. `namespace overridden_adders`) and then force that one to be used through a `using` statement. — CompuChip, Feb 27 '14 at 11:20
Wht do you mean by saying "override definition"? Do you want to overload this function, i.e. to provide a function with different parameters? Or do you want do define another function with exactly the same signature? — Igor R., Feb 27 '14 at 11:24
@JaredBeekman It's an [unnamed namespace](http://stackoverflow.com/questions/4422507/superiority-of-unnamed-namespace-over-static). — Joseph Mansfield, Feb 27 '14 at 11:27
@Igor R.: Its not overloading. Parameters and function name remains the same only the definition of the function needs to be changed. — Ritesh Kumar Gupta, Feb 27 '14 at 11:27
Ok, I see - you want another function to be called from within `getsum`. No, it's not possible without really dirty preprocessors tricks. The person who wrote it didn't intend to make it polymorphic. — Igor R., Feb 27 '14 at 11:30
@IgorR.: It is possible, check my anwser. The code is still... dodgy, to say the least. — gwiazdorrr, Feb 27 '14 at 11:51

gwiazdorrr · Answer 1 · 2014-02-27T11:43:21.540

Turns out it is possible without altering any of the headers and preprocessor magic!

Since your getsum is in an unnamed namespace, you can define calculate_addition_h function in the unnamed namespace before including addition.h:

main.cpp

namespace
{
    int calculate_addition_h(int p, int q)
    {
        return 666;
    }
}

#include "addition.h"
#include <iostream>
int main(){
    int x=2;
    int y=3;
    std::cout<<getsum(x,y);
}

In C++, functions in same namespace take precedence over functions in parent namespaces. In this case parent namespace is the global one.

score 0 · Answer 2 · answered Feb 27 '14 at 11:24

0

As you are using global function, so it is not possible to override the function as it can be done in class. Its better to define a new function with the same name inside a different namespace

answered Feb 27 '14 at 11:24

rajenpandit

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Overriding function from caller source file in C++

2 Answers2