Weird characters in printf - ios

Question

My environment: Xcode5, iOS, Objective-C/Objective-C++ mix.
I am trying to figure out what causes the next problem. I am writing my own logging function:
int _me_log(const char *fmt, ...) {
va_list args;
va_start(args, fmt);
char *c = va_arg(args, char *);
char *message = NULL;
printf(fmt, args);
int n = asprintf(&message, fmt, args);
if (n != -1 && message != NULL) {
//do something with 'message' like writing to file, etc.
UPDATE:
//we need to handle memory created for 'message' storage.
free(message);
}
va_end(args);
return n;
}
Then I call it like this:
_me_log("socket %s did open", "Socket: 0x1fd1c880");
And instead of correct output socket Socket: 0x1fd1c880 did open I get some gibberish like this socket \\323\331/ did open in this line printf(fmt, args);.
If I call it this way printf("%s", c); I get correct results.
I have googled several implementations (this or this ) of logging functions and functions which pass variable parameters and it seems that I do everything correctly.
Could you please suggest me what I'm doing wrong?

Answer 1

You've got the right idea to use va_list here, but if you work with va_list you should use vasprintf instead of asprintf:
int _me_log(const char *fmt, ...)
{
va_list args;
char *message = NULL;
int n;
va_start(args, fmt);
n = vasprintf(&message, fmt, args);
if (n != -1 && message != NULL) {
// ... use message ...
}
free(message);
va_end(args);
return n;
}
For every routine of the printf family, there is a variant that takes a va_list instead of the variadic argument ... and whose name is prefixed with the letter v, for example:
int printf(const char *format, ...);
int vprintf(const char *format, va_list ap);
These routines exist so you can write you own (non-macro) wrapper for xprintf.

Answer 2

Seems like a very complicated implementation. Try:
int _me_log(const char *fmt, ...) {
int ret = 0;
va_list va;
va_start(va, fmt);
ret = vprintf(fmt, va);
va_end(va);
putc('\n', stdout);
return ret;
}
But, of course, that is no different from printf(), except for forcing a newline.