https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67386
--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- On Fri, 28 Aug 2015, msebor at gcc dot gnu.org wrote: > GCC isn't completely consistent in diagnosing references to undeclared > functions. In the test case below, it issues an error for only the last three > out of the four definitions of foo. It issues a warning for the first one, > even though it too references an undeclared identifier. This is a consequence of C90 implicit declarations being accepted as an extension in C11 mode. The implicit declaration from the call in the first case is in scope for the non-call reference. In no other case is there a declaration, even implicit, in scope for such a reference. > Versions prior to 5.1 diagnosed only the second and fourth forms. Previous versions defaulted to gnu89. In C99 and later, each half of an if statement has its own scope; before C99, the scope of the implicit declaration in case 3 would have been the whole of the body of the function.
