Using Goto function across different functions

Question

How can I use goto across different functions? For example:

int main() {
    // ....
    REACH:
    // ....
}
    
void function() {
    goto REACH;
}

Answer 1

You can't in Standard C++. From $6.6.4/1 of the C++ Language Standard

The goto statement unconditionally transfers control to the statement labeled by the identifier. The identifier shall be a label (6.1) located in the current function.

...or in Standard C. From $6.8.6.1/1 of the C Language Standard

The identifier in a goto statement shall name a label located somewhere in the enclosing function. A goto statement shall not jump from outside the scope of an identifier having a variably modified type to inside the scope of that identifier.

Answer 2

You can't in Standard C; labels are local to a single function.

The nearest standard equivalent is the setjmp() and longjmp() pair of functions.

GCC has extensions to support labels more generally.

Answer 3

For gcc:

#include <iostream>

void func(void* target){
    std::cout << "func" <<std::endl;
    goto *target;
}


int main() {
    void* target;
    auto flag = true;
l:
    std::cout << "label" <<std::endl;
    target = &&l;
    if (flag) {
        flag = false;
        func(target);
  }
}

Note that this can be an undefined behavior

Answer 4

You can't. Think of this. There is a function A which is recursively calling another function B which in turn is calling A. Now, suppose that you put a goto statement from A to B. The question now becomes which instance of A do you want to go to which is undefined. Also, if no previous instance of A is defined, you have a bigger problem of no initialized variables in the function that are present before the label.

#include "bits/stdc++.h"
int i=0;
A(){
run:
    B();
}
B(){
if(i==10)
    goto run;
i++;
A();
}