https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67386
--- Comment #4 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- On Fri, 28 Aug 2015, msebor at gcc dot gnu.org wrote: > My reading was that the implicit declaration is intended to be in effect only > for the call to the otherwise undeclared function, but GCC and the other > compilers I've tried let it persist (at least) until the end of the scope and Yes (remember, two scopes are the same if they end at the same point; saying what block the declaration appears in is the same as saying where it ends). > I think Clang and IBM xlc are both wrong since the reference to abs on line 8 > should clearly be diagnosed. The C90 words aren't completely clear about > where > in the innermost block the extern int identifier(); declaration is supposed to > appear but it stands to reason that it should appear where all other > declarations must appear in C90: before any executable code. So diagnosing > the In general, it's a mistake to interpret "X is equivalent to Y" statements in the C standard as referring to a textual substitution; there are plenty of other places where applying such a substitution goes wrong. Cf. cases where something is said to be equivalent to a particular sequence of declarations and statements and it must be implicitly understood that the variable names in those declarations and statements are not special in any way.
