-std=c99

[Bill Pursell]

On Linux, <features.h> states that #define _GNU_SOURCE implies 
_ISOC99_SOURCE.  Code that includes:
for (int i=0; ...)
compiles fine with
gcc -std=c99 ...
but does not compile without the explicit -std flag, instead generating 
the error: 'for' loop initial declaration used outside C99 mode

I had hoped that #define _GNU_SOURCE would allow compilation without the 
-std flag.  Is there a way to structure the code so that the -std flag 
is not necessary?