Modify printf()s via macro to include file and line number information

Question

I was just wondering if there is some macro-hack we can use, to alter existing printf() statements in a project.

/* file.c */
printf ("%s", strerror(errno));

/* After macro processing, this line would become */
printf ("%s %s %d", strerror(errno), __FILE__, __LINE__);

Answer 1

With the caveat in my comment, you could do it using a variadic macro:

#define PRINTF_FL(format, ...) \
    printf(format " %s %d", __VA_ARGS__, __FILE__, __LINE__)

Answer 2

Try this:

#define debug(fmt, ...) printf("%s:%d: " fmt, __FILE__, __LINE__, __VA_ARGS__);

I used name debug instead of printf, because I don't think you should override standard functions. You could break something.

Use this like:

debug("This is debug no %d", 5);

To get output similar to:

program.c:12: this is debug no 5

(file: program.c, line: 12).

Answer 3

And here is my "half penny".

Function name & debug messages:

// debug mode, -DEBUG
#ifdef EBUG
    #define FNAME() fprintf(stderr, "\n%s (%s, line %d)\n", __func__, __FILE__, __LINE__)
    #define DBG(...) do{fprintf(stderr, "%s (%s, line %d): ", __func__, __FILE__, __LINE__); \
                    fprintf(stderr, __VA_ARGS__);           \
                    fprintf(stderr, "\n");} while(0)
#else
    #define FNAME()  do{}while(0)
    #define DBG(...) do{}while(0)
#endif //EBUG

Use macro FNAME() to show just name of function & file/line, DBG(text) to show printf-like debug message with info about function name & file/line.

And something that may be useful for coloured debug & error/warning messages.

In header file:

extern int globErr;
#define ERR(...) do{globErr=errno; _WARN(__VA_ARGS__); exit(-1);}while(0)
#define WARN(...) do{globErr=errno; _WARN(__VA_ARGS__);}while(0)
#define WARNX(...) do{globErr=0; _WARN(__VA_ARGS__);}while(0)
// functions for color output in tty & no-color in pipes
EXTERN int (*red)(const char *fmt, ...);
EXTERN int (*_WARN)(const char *fmt, ...);
EXTERN int (*green)(const char *fmt, ...);

In C file:

int globErr = 0; // errno for WARN/ERR
// pointers to coloured output printf
int (*red)(const char *fmt, ...);
int (*green)(const char *fmt, ...);
int (*_WARN)(const char *fmt, ...);
/*
 * format red / green messages
 * name: r_pr_, g_pr_
 * @param fmt ... - printf-like format
 * @return number of printed symbols
 */
int r_pr_(const char *fmt, ...){
    va_list ar; int i;
    printf(RED);
    va_start(ar, fmt);
    i = vprintf(fmt, ar);
    va_end(ar);
    printf(OLDCOLOR);
    return i;
}
int g_pr_(const char *fmt, ...){
    va_list ar; int i;
    printf(GREEN);
    va_start(ar, fmt);
    i = vprintf(fmt, ar);
    va_end(ar);
    printf(OLDCOLOR);
    return i;
}
/*
 * print red error/warning messages (if output is a tty)
 * @param fmt ... - printf-like format
 * @return number of printed symbols
 */
int r_WARN(const char *fmt, ...){
    va_list ar; int i = 1;
    fprintf(stderr, RED);
    va_start(ar, fmt);
    if(globErr){
        errno = globErr;
        vwarn(fmt, ar);
        errno = 0;
        globErr = 0;
    }else
        i = vfprintf(stderr, fmt, ar);
    va_end(ar);
    i++;
    fprintf(stderr, OLDCOLOR "\n");
    return i;
}

const char stars[] = "****************************************";
/*
 * notty variants of coloured printf
 * name: s_WARN, r_pr_notty
 * @param fmt ... - printf-like format
 * @return number of printed symbols
 */
int s_WARN(const char *fmt, ...){
    va_list ar; int i;
    i = fprintf(stderr, "\n%s\n", stars);
    va_start(ar, fmt);
    if(globErr){
        errno = globErr;
        vwarn(fmt, ar);
        errno = 0;
        globErr = 0;
    }else
        i = +vfprintf(stderr, fmt, ar);
    va_end(ar);
    i += fprintf(stderr, "\n%s\n", stars);
    i += fprintf(stderr, "\n");
    return i;
}
int r_pr_notty(const char *fmt, ...){
    va_list ar; int i;
    i = printf("\n%s\n", stars);
    va_start(ar, fmt);
    i += vprintf(fmt, ar);
    va_end(ar);
    i += printf("\n%s\n", stars);
    return i;
}

In main():

if(isatty(STDOUT_FILENO)){ // make color output in tty
    red = r_pr_; green = g_pr_;
}else{ // no colors in case of pipe
    red = r_pr_notty; green = printf;
}
if(isatty(STDERR_FILENO)) _WARN = r_WARN;
else _WARN = s_WARN;

After that you will be able to use coloured output in case running in terminal and non-coloured in case of pipe. Functions red and green are analogues of printf for coloured output. Function _WARN used in macros to show user message and string for errno: ERR for case of errors (ends with exit), WARN — analogue of ERR but without exit and WARNX to show messages without errno.