GCC - Preserving statement expression results on stack

[Andrew Haley]

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.

Andrew.