I want to implement a function Myprintf() that takes arguments like printf().
Now I am doing this by:
sprintf(demoString, "Num=%d String=%s", num, str);
Myprintf(demoString);
I want to replace this function call as:
Myprintf("Num=%d String=%s", num, str);
How is this possible?
#include <stdio.h>
#include <stdarg.h>
extern int Myprintf(const char *fmt, ...);
int Myprintf(const char *fmt, ...)
{
char buffer[4096];
va_list args;
va_start(args, fmt);
int rc = vsnprintf(buffer, sizeof(buffer), fmt, args);
va_end(args);
...print the formatted buffer...
return rc;
}
It isn't clear from your question exactly how the output is done; your existing Myprintf() presumably outputs it somewhere, maybe with fprintf(). If that's the case, you might write instead:
int Myprintf(const char *fmt, ...)
{
va_list args;
va_start(args, fmt);
int rc = vfprintf(debug_fp, fmt, args);
va_end(args);
return rc;
}
If you don't want to use the return value, declare the function as void and don't bother with the variable rc.
This is a fairly common pattern for 'printf() cover functions'.
The printf and its relatives are in a family of functions called variadic functions and there are macros/functions in the <stdarg.h> header in the C standard library to manipulate variadic argument lists. Look at the GNU docs for examples: How Variadic Functions are Defined and Used.
You need to define a function with variable arguments, and use vsprintf to build the string.
