Re: question related to passing variable number of arguments

On Wed, 19 Sep 2007 00:55:35 -0700, "junky_fellow@xxxxxxxxxxx"
<junky_fellow@xxxxxxxxxxx> wrote:

Hi,

I want to define a function log_file(), that would print the
formatted message to stdout if the FILE pointer passed is NULL else
print the formatted output to the file corresponding to FILE*.

For eg.

extern FILE *fp;

int main(void)
{
int n1=0;
int n2=100;

log_file(fp, "SOME MESSAGE n1=%d n2=%d\n", n1, n2);
}

I want that, log_file() should print the formatted output to stdout,
in case fp is NULL, else
print the output to the corresponding file.
Can some one please help ? I tried my best, but could not find any
solution.

thanks a lot for any help.

Hi junky fellow,

The following doesn't deal with your extern fp, because it represents
a single translation unit that compiles and links. Nevertheless, I
hope it gives you an idea of how you can solve your problem.

#include <stdarg.h>
#include <stdio.h>

#define MAX_MSG_LENGTH 256 /*or whatever size you need*/

static FILE *G_fp = NULL;
static void log_file(FILE *fp, const char *format, ...);

int main(void)
{
int n1 = 0;
int n2 = 100;

log_file(G_fp, "SOME MESSAGE n1 = %d and n2 = %d\n", n1, n2);
return 0;
}

static void log_file(FILE *fp, const char *format, ...)
{
va_list arg_ptr;
char text[MAX_MSG_LENGTH + 1];

va_start(arg_ptr, format);
vsprintf(text, format, arg_ptr);
va_end(arg_ptr);
if ( fp )
{
fprintf(fp, "%s", text);
}
else
{
fprintf(stdout, "%s", text);
}
}

Regards
--
jay
.

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