Is there a printf converter to print in binary format?

Question

I can print with printf as a hex or octal number. Is there a format tag to print as binary, or arbitrary base?

I am running gcc.

printf(\"%d %x %o         


        

Answer 1

Here's a version of the function that does not suffer from reentrancy issues or limits on the size/type of the argument:

#define FMT_BUF_SIZE (CHAR_BIT*sizeof(uintmax_t)+1)

char *binary_fmt(uintmax_t x, char buf[static FMT_BUF_SIZE])
{
    char *s = buf + FMT_BUF_SIZE;
    *--s = 0;
    if (!x) *--s = '0';
    for (; x; x /= 2) *--s = '0' + x%2;
    return s;
}

Note that this code would work just as well for any base between 2 and 10 if you just replace the 2's by the desired base. Usage is:

char tmp[FMT_BUF_SIZE];
printf("%s\n", binary_fmt(x, tmp));

Where x is any integral expression.