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variable arguments in C

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Re: variable arguments in C

#11

Jul 16th, 2007

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Originally Posted by dr4g

Haha, i thought he ment passing variable arguments.. as you can pass an array as a parameter (using pointers of course), so i thought he ment how do you pass a variable to a function.

Oh well

Oh, now I understand the reason for your post.

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Originally Posted by hitesh_mathpal

Dear friend , I am asking about a function like printf(). as it takes the variable argument.How can we define a function like this?

Most functions that take a variable number of arguments are declared with at least one real argument followed by three periods, like the code posted by Narue and TkTkorrovi.

printf() does not use the periods because of the format parameter which indicates the number of arguments and their data types.

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Narue

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Re: variable arguments in C

#12

Jul 16th, 2007

>Most functions that take a variable number of arguments are declared
>with at least one real argument followed by three periods
All of them, actually.

va_start requires the last non-variadic parameter as its second argument, so at least one non-variadic parameter is required as well as the ellipsis to specify further variadic parameters.

>printf() does not use the periods because of the format parameter
>which indicates the number of arguments and their data types.
Since when? This is the prototype for printf, and I see an ellipsis:

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
int printf ( const char *format, ... );
int printf ( const char *format, ... );

The format string is for evaluating the variadic parameters, it's not a replacement for the required syntax.

I'm here to prove you wrong.

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Re: variable arguments in C

#13

Jul 16th, 2007

Narue: thanks for the correction

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Re: variable arguments in C

#14

Jul 16th, 2007

It's tested now

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
#include <stdio.h>
#include <stdarg.h>
 
void stringstofile (FILE *fp, ...)
{
        char *p;
        va_list ap;
 
        va_start (ap, fp);
        while ((p = va_arg (ap, char *)))
                fprintf (fp, "%s\n", p);
        va_end (ap);
}
 
int main ()
{
        stringstofile (stdout, "one",
                "two", "three", NULL);
        return 0;
}
#include <stdio.h>
#include <stdarg.h>

void stringstofile (FILE *fp, ...)
{
        char *p;
        va_list ap;

        va_start (ap, fp);
        while ((p = va_arg (ap, char *)))
                fprintf (fp, "%s\n", p);
        va_end (ap);
}

int main ()
{
        stringstofile (stdout, "one",
                "two", "three", NULL);
        return 0;
}