This only applies to a situation where you have a function that requires dynamic checks for preconditions. I would suggest that such a function (or how it's being used) is likely a blight already, but tolerable with very few call sites. In which case checking at the call site is the right move. And as you continue to abuse the function perhaps the code duplication will prompt you to reconsider what you are doing.
If there is a performance implication of moving the if into the callers or not, you can do it with an inline function.
static inline int function(blob *ptr, int arg)
{
if (ptr == NULL)
return ERR_NULL;
return real_function(ptr, arg);
}
ISO C allows:
free(NULL); // convenient no-op, does nothing
fflush(NULL); // flush all streams; done implicitly on normal exit
time(NULL); // don't store time_t into a location, just return it
strtol(text, NULL, 10); // not interested in pointer to first garbage char
setbuf(stream, NULL); // allocate a buffer for stream
realloc(NULL, size); // behave like malloc(size)
sigprocmask(SIG_UNBLOCK, these_sigs, NULL); // not interested in previous signal mask
CreateEventA(NULL, FALSE, FALSE, NULL); // no security attributes, no name
So if a function dereferences a pointer, it doesn't make sense to check that it's not null inside the function?
Unless there's an actual performance implication, this is all purely a matter of taste. This is the kind of broadly true, narrowly false stuff that causes people to destroy codebases. "I can't write it this way, because I have to push ifs up and fors down!!!" It's a totally fake requirement, and it imposes a fake constraint on the design.