#define with Variable arguments for debugging

Question

I have prints available something like this

PrintMe(("abc %d",a));

Printme defined like this

#define Printme(_X_) printf _X_

But now i need to map it with some print which takes variable arguments something like

#define Printme(format , args ....)   PrintVar(30,format,##args)

Printvar has single parentheses and Printme has double parentheses

How to map this

Is there a reason you're using preprocessor macros instead of a normal function? — ipavl
– ipavl, Commented Oct 30, 2014 at 2:58
See this post for details on defining debug macros in c stackoverflow.com/questions/1644868/…. — Paul Rooney
– Paul Rooney, Commented Oct 30, 2014 at 2:59

John Zwinck · Accepted Answer · 2014-10-30 03:26:37Z

1

You can do this:

#define Printme(format, ...)   PrintVar(30, format, ##__VA_ARGS__)

Documentation (for GCC): https://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html

edited Oct 30, 2014 at 3:26

answered Oct 30, 2014 at 3:02

John Zwinck

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3 Comments

Gajukorse Over a year ago

But Printme has a format like Printme(("abc")); Printvar is like PrintVar(30, "abc") since its legacy code i cant change format of Printme

John Zwinck Over a year ago

@Gajanana: OK, I've updated my answer to use the special ## before __VA_ARGS__ which makes it work in the case where you have a format string and no additional arguments.

Gajukorse Over a year ago

Problem is Printme ha double Parentheses and PrintVar has single. So its not working –

n0p · Accepted Answer · 2014-10-30 08:33:16Z

0

How about:

#define PRINTME2(fmt, ...) printvar(30, fmt, ##__VA_ARGS__)
#define PRINTME(_X_) PRINTME2 _X_

A complete example:

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

void printvar(int lvl, char * fmt, ...)
{
    printf("lvl %d:", lvl);                                                                         
    va_list argptr;
    va_start(argptr,fmt);
    vprintf(fmt, argptr);
    va_end(argptr);
}

#define PRINTME2(fmt, ...) printvar(30, fmt, ##__VA_ARGS__)
#define PRINTME(_X_) PRINTME2 _X_

int main(void)
{
    PRINTME(("I have %u apples\n", 3));
    return 0;
}

Output:

lvl 30:I have 3 apples

answered Oct 30, 2014 at 8:33

n0p

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