Thread: make printf using printf?

va_start(), va_arg(), and va_end() are definitely good things to look at. Check out the man pages for them for explanations and examples.

Here's a really sad one that only handles %d and %s without any precision modifiers and doesn't return any value:

Code:

itsme@itsme:~/C$ cat myprintf.c
#include <stdio.h>
#include <stdarg.h>

void myprintf(char *fmt, ...)
{
  char *p;
  va_list ap;

  va_start(ap, fmt);

  for(p = fmt;*p;p++)
  {
    if(*p != '%')
      putchar(*p);
    else
    {
      p++;
      switch(*p)
      {
        case 'd':
        {
          int num = va_arg(ap, int);
          int mult, init = 0;

          if(num < 0)
          {
            putchar('-');
            num *= -1;
          }
          for(mult = 1000000000;mult > 0;mult /= 10)
            if(init || num/mult%10)
            {
              putchar(num/mult%10+'0');
              init = 1;
            }
          break;
        }
        case 's':
        {
          char *s = va_arg(ap, char *);

          while(*s)
            putchar(*s++);
          break;
        }
        default:
          putchar(*p);
      }
    }
  }

  va_end(ap);
}

int main(void)
{
  myprintf("%d %s %s %d %s %s...\n",
    4, "score", "and", 7, "years", "ago");
  return 0;
}
itsme@itsme:~/C$ ./myprintf
4 score and 7 years ago...
itsme@itsme:~/C$

Well, I can see why the %d and %s ones wouldn't be giving you any trouble...I did them for you. If I helped with those other two then I'm afraid you wouldn't bother learning anything. What (specifically) are you having problems with in those two?

%x expects an integer value. Something like printf("%x\n", 0x8c);

I'm not against helping, but your question was too vague to give you an answer without doing the whole thing for you. Your last question was about something specific and I was able to answer it.