On Thu, 2007-08-30 at 10:31 +0100, Andrew Haley wrote: > Joe Perches writes: > > I know that gcc preserves stack slots for statement expressions. > > http://gcc.gnu.org/ml/gcc-patches/2002-02/msg00958.html > > What about statement expressions that return arrays? > > When does GCC free stack used by statement expression array returns? > > For instance: > > #define itoa(i) \ > > ({ char tmp[16]; sprintf(tmp, "%d", i); tmp; }) > > printf("%s %s\n", itoa(1), itoa(2)); > > is the printf output guaranteed to be "1 2" or is it undefined? > > ISO/IEC 9899:1999 (E) > > 6.2.1 Scopes of identifiers > > 2 For each different entity that an identifier designates, the > identifier is visible (i.e., can be used) only within a region of > program text called its scope. > > Unless you see some gcc documentation to the contary, that's the rule. Statement expressions are gcc extensions, ISO scoping rules don't necessarily apply. Is this guaranteed? #define SE_identity(i) ({ typeof (i) x = i; x;}) printf("%d %d\n", SE_identity(1), SE_Identity(2)); Output: "1 2"
