How to use C89 with certain C99 features

[Steffen Dettmer]

* On Tue, Apr 5, 2011 at 4:02 PM,  <richardcavell@mail.com> wrote:
> That's what I'm thinking.  I can't figure out how to provide the
> functionality I need using C89.  The functionality I need is:
>
> 1.  Variadic macros, which allows me to do this:
>
> #define myprintfwrapper (A,...) myfunc (__FILE__,__LINE__,A,__VA_ARGS__)
> void myfunc (char *szfile, int line, A, ...);

We have such situations where the platforms w/o vaargs are
"small" anyway and the overhead for __FILE__ in the binaries is
bad anyway, so simple solution is to simply on those platforms do
/not/ use file and line; two implementations of myfunc: one with
file and line (f_l), other without, called by "double-brace-macros".

Here an example.

  #if HAVE_VAARGS

  #define myprintf(args) myTemp args
  #define myTemp(fmt, args...) myprintfunc_f_l(__FILE__, __LINE__, fmt, ## args)
  int myprintfunc_f_l(const char *file, int line, const char *fmt, ...);

  #else /* no HAVE_VAARGS */

  #define myprintf(args) myprintfunc args
  int myprintfunc(const char *fmt, ...);

  #endif /* no HAVE_VAARGS */

  you'd use the macro with double braces:

  int func(void)
  {
  	mypriuntf(("Hello, %s\n!", world));
  }

of course for main development and debugging it is suited to use
a platform with vaargs, but the other platforms at least do work
(just do not print __FILE__ and __LINE__, but the message).

If you have a platform without elipsis and very limited resources
you could even redefine __FILE__ to a "file counter" (short
number for each file or use MYFILENUMBER) and log only __FILE__
and __LINE__ which for error logging sometimes is a small bit
better than nothing.

> 2.  Struct initialization with run-time data, which allows
> const members of the struct to contain run-time data.  I make
> the members const for efficiency and error prevention.

> If anyone can figure out how to do those things with C89, let me know.

when having e.g.:

 function func(long seconds)
 {
       struct timeval t = { seconds, 0 };
 }

you should to use

 function func(long seconds)
 {
       struct timeval t = { 0 };
       t.tv_sec = seconds;
 }


oki,

Steffen