printf.c

   1 #include "types.h"
   2 #include "stat.h"
   3 #include "user.h"
   4
   5 static void
   6 putc(int fd, char c)
   7 {
   8   write(fd, &c, 1);
   9 }
  10
  11 static void
  12 printint(int fd, int xx, int base, int sgn)
  13 {
  14   static char digits[] = "0123456789ABCDEF";
  15   char buf[16];
  16   int i, neg;
  17   uint x;
  18
  19   neg = 0;
  20   if(sgn && xx < 0){
  21     neg = 1;
  22     x = -xx;
  23   } else {
  24     x = xx;
  25   }
  26
  27   i = 0;
  28   do{
  29     buf[i++] = digits[x % base];
  30   }while((x /= base) != 0);
  31   if(neg)
  32     buf[i++] = '-';
  33
  34   while(--i >= 0)
  35     putc(fd, buf[i]);
  36 }
  37
  38 // Print to the given fd. Only understands %d, %x, %p, %s.
  39 void
  40 printf(int fd, char *fmt, ...)
  41 {
  42   char *s;
  43   int c, i, state;
  44   uint *ap;
  45
  46   state = 0;
  47   ap = (uint*)(void*)&fmt + 1;
  48   for(i = 0; fmt[i]; i++){
  49     c = fmt[i] & 0xff;
  50     if(state == 0){
  51       if(c == '%'){
  52         state = '%';
  53       } else {
  54         putc(fd, c);
  55       }
  56     } else if(state == '%'){
  57       if(c == 'd'){
  58         printint(fd, *ap, 10, 1);
  59         ap++;
  60       } else if(c == 'x' || c == 'p'){
  61         printint(fd, *ap, 16, 0);
  62         ap++;
  63       } else if(c == 's'){
  64         s = (char*)*ap;
  65         ap++;
  66         if(s == 0)
  67           s = "(null)";
  68         while(*s != 0){
  69           putc(fd, *s);
  70           s++;
  71         }
  72       } else if(c == 'c'){
  73         putc(fd, *ap);
  74         ap++;
  75       } else if(c == '%'){
  76         putc(fd, c);
  77       } else {
  78         // Unknown % sequence.  Print it to draw attention.
  79         putc(fd, '%');
  80         putc(fd, c);
  81       }
  82       state = 0;
  83     }
  84   }
  85 }