Call a function without argument, although it needs one [K&R-C]

Question

It\'s K&R-C and here is the code: http://v6shell.org/history/if.c

Look at the main-Method. There is this line \"if(exp())\".

But the function exp is decl

Answer 1

Ultimately, it is a bug in the Unix V6 shell support command, if.

The code for the function is:

exp(s) {
    int p1; 

    p1 = e1();
    if (eq(nxtarg(), "-o")) return(p1 | exp());
    ap--;
    return(p1);
}

The function parameter s, implicitly of type int (as is the function iteself), is actually unused in the function, so the bug is the presence of s, not the absence of an argument in the calls to exp(). All the calls with zero actual arguments are correct.