Recursion and static variables [duplicate]

Question

So I was preparing for an entrance exam here in India when I came across this piece of C code

#include <stdio.h>
int main(void) {
    static int i = 4;
    if (--i) {
        main();
        printf("%d", i);
    }
}

I thought the printf statement never gets executed and the output will be blank. But I saw the answer to be 0000 and that this happens due to the static keyword with the int.

Can anyone explain why the printf executes or is that guy wrong?

Answer 1

In the context of the question being about recursion, it will print out "000" (I don't know why the answer shows 4 zeros because with '--i' decrement happens before assignment). If you unroll the calls you get:

if (--i) { //i == 3
    if (--i) { //i == 2
        if (--i) { //i == 1
            if (--i) { //i == 0
                // rest does not get evaluated since the condition is false
            }
            printf("%d", i); // i is 0 now
        }
        printf("%d", i); //i is still 0
    }
    printf("%d", i); //i is still 0
}

However like most have mentioned this code sucks and I would advise you never consider this level of sloppiness for any software you write.

Answer 2

It is legal to recurse on main in C^* (although why would you?)

Additionally, C11 (5.1.2.2.1) states:

It shall be defined with a return type of int ... [or] If the return type is not compatible with int, the termination status returned to the host environment is unspecified.

(C++ states that the return type must be int)

So this portion of the code is actually standard-compliant, but the actual return is implementation-defined (thanks @chux)

Can anyone explain why the printf executes or is that guy wrong?

If you're compiling C with a C++ compiler, guy is wrong. Otherwise the code will compile.

Now that this is out of the way, the printf will indeed execute because the static variable is only ever initialized once, as per 6.2.4/3

An object whose identifier is declared [...]with the storage-class specifier static has static storage duration. Its lifetime is the entire execution of the program and its stored value is initialized only once, prior to program startup

^{*It is definitely NOT legal in C++. From [basic.start.main]: "The function main shall not be used within a program". There's a lot of C++ asides in this answer because the question was originally tagged as C++ and the information is useful}