On Mon, Mar 8, Bob Friesenhahn <bfriesen@xxxxxxxxxxxxxxxxxxx> wrote:
> It is also interesting to note that it is usually ok for the
> content of the header file to be parsed any number of times.
> The only exception might be with some weird macro expansion
> (but that would be a bug).
>
> The conditional inclusion of content is only an optimization.
If you have a struct definition (C/C++) or a typedef (C) in the
.h file, C compilers may refuse to process it twice and an
inclusion guard is needed:
user@host # cat x.h
typedef int counter_t;
user@host # cat x.c
#include "x.h"
#include "x.h"
int main(void) { return 0; }
user@host # gcc x.c
In file included from x.c:2:
x.h:1: redefinition of `counter_t'
x.h:1: `counter_t' previously declared here
user@host # tcc x.c
x.h:1: Error: duplicate typedef 'counter_t'
x.c: 0 warnings, 1 error, 0 serious errors
oki,
Steffen
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