The Answer to the Ultimate Question of Life, the Universe, and Everything

You are given a partially specified program.

Make the program print 42. You must not modify the code beyond what you are told you can modify.

This problem is only available in C++.

The judge will run your code in a form that looks similar to the following:

#include <cstdio>

void foo(/* fill in blanks */) {
    /* fill in blanks */
}

int main() {
    const int* x;
    USER_CALL(x);
    std::printf("%d\n", *x);
    return 0;
}

• USER_CALL(x) is a macro you must define so that the judge calls foo correctly.
• In other words: USER_CALL(x) should expand to the actual function call (e.g., if x was an int and foo takes an int pointer, you might define #define USER_CALL(x) foo(&x)).

Requirements

• The program must have defined behavior.

• The value printed must always be 42, regardless of optimization level.

• Returning or storing the address of a local (stack) variable is not allowed, even if it appears to work.

• You may not modify main.

• You may choose the function signature of foo and how it is called.

• No input or output other than the final printed integer.