[dbrower]

It doesn't have to be the NULL macro, which is correctly defined as plain 0.

The literal 0 is treated specially, so this could indeed be one of those 'turns into a weird bit pattern NULL pointers', if such a thing existed in the wild anymore.

But you're correct in that there probably haven't been any since the turn of the century or whenever the last Univac mainframes got turned off.

[pests]

Apparently according to the c-faqs link elsethread

    execl takes a variable-length, null-pointer-terminated list of character pointer arguments, and is correctly called like this:
    execl("/bin/sh", "sh", "-c", "date", (char *)0);

Due to ececl being a variadic function it can not take advantage of a prototype to instruct the compiler that one of its arguments needs to be treated as a pointer context.