The problem is that GCC does not give an error (only a warning)
even for
things like this where it should be trivial to detect that the
usage *is*
uninitialized, not just might be:
int foo(void)
{
int a;
return a;
}
The compiler must not reject this code, because the undefined
behavior
only occurs if executed. There is no constraint violated.
Fine (though GCC could have something similar to -Werror but more
limited in scope to the really serious stuff that *should* be
illegal even if it isn't), but it should at least be a separate
warning class.
My point was to counter Segher's assertion that the compiler
currently gives an error on the obvious stuff.
I never said that, or didn't intend to anyway; what I was trying to say
is that the compiler makes a difference between cases where it knows
something is uninitialized vs. cases where it cannot prove either way:
$ cat mm.c
int bork(void)
{
int a;
return a;
}
int main(void)
{
return bork();
}
$ powerpc-linux-gcc -Wall -W -Os -c mm.c
mm.c: In function 'bork':
mm.c:5: warning: 'a' is used uninitialized in this function
Note: _is_ used uninitialized, not "may be" like in cases where the
compiler
isn't sure.
I don't know why this isn't an error; perhaps GCC does not assume main
() to
always be executed. I don't think it could prove much anything to be
executed in non-toy examples, anyway.
Segher
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