How to set a breakpoint in GDB where the function returns?

Question

I have a C++ function which has many return statements at various places. How to set a breakpoint at the return statement where the function actually returns ?

And

Answer 1

If you can change the source code, you might use some dirty trick with the preprocessor:

void on_return() {

}

#define return return on_return(), /* If the function has a return value != void */
#define return return on_return()  /* If the function has a return value == void */

/* <<<-- Insert your function here -->>> */

#undef return

Then set a breakpoint to on_return and go one frame up.

Attention: This will not work, if a function does not return via a return statement. So ensure, that it's last line is a return.

Example (shamelessly copied from C code, but will work also in C++):

#include 

/* Dummy function to place the breakpoint */
void on_return(void) {

}

#define return return on_return()
void myfun1(int a) {
    if (a > 10) return;
    printf("<10\n");
    return;   
}
#undef return

#define return return on_return(),
int myfun2(int a) {
    if (a < 0) return -1;
    if (a > 0) return 1;
    return 0;
}
#undef return


int main(void)
{
    myfun1(1);
    myfun2(2);
}

The first macro will change

return;

to

return on_return();

Which is valid, since on_return also returns void.

The second macro will change

return -1;

to

return on_return(), -1;

Which will call on_return() and then return -1 (thanks to the ,-operator).

This is a very dirty trick, but despite using backwards-stepping, it will work in multi-threaded environments and inlined functions, too.