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52

answers:

3

Are Statement and Declarations in Expressions specific to GNU C ? Or this feature is also included in C99 standard ?

+2  A: 

It's a GCC extension. (See the GCC docs, e.g. here for gcc 4.3.3, for a full list of GCC extensions; and the C99 spec is available here.)

GCC will warn about such things if you use the -pedantic -std=c99 flags, e.g.:

$ cat foo.c
int main(void)
{
  return ({ int a = 0; a; });
}
$ gcc -pedantic -std=c99 -c foo.c
foo.c: In function 'main':
foo.c:3: warning: ISO C forbids braced-groups within expressions
Matthew Slattery
Is the feature included in the C99 standard as well ?
Andrei Ciobanu
No -- it isn't.
Matthew Slattery
(I've updated my answer to clarify that.)
Matthew Slattery
+1  A: 

It's a GNU C extension. That's what they mean by "may appear ... in GNU C." (my emphasis)

R Samuel Klatchko
Is the feature included in the C99 standard as well ?
Andrei Ciobanu
@AndreiCiobanu - no, it's limited to GNU C only (as opposed to standard C)
R Samuel Klatchko
+1  A: 

While this is not a C99 standard, this extension is not specific to gcc either.

For instance, the clang compiler and Intel C++ compiler support this extension.

KennyTM