stdio.c

   1 #include <stdarg.h>
   2 #include <stdio.h>
   3 #include <unistd.h>
   4
   5 static char *putstr(char *d, char *s)
   6 {
   7         while (*s)
   8                 *d++ = *s++;
   9         return d;
  10 }
  11
  12 static int digits(unsigned long n, int base)
  13 {
  14         int i;
  15         for (i = 0; n; i++)
  16                 n /= base;
  17         return i ? i : 1;
  18 }
  19
  20 static char *digs = "0123456789abcdef";
  21
  22 static char *putint(char *s, unsigned long n, int base, int sign)
  23 {
  24         int d;
  25         int i;
  26         if (sign && n & 0x80000000) {
  27                 *s++ = '-';
  28                 n = -n;
  29         }
  30         d = digits(n, base);
  31         for (i = 0; i < d; i++) {
  32                 s[d - i - 1] = digs[n % base];
  33                 n /= base;
  34         }
  35         return s + d;
  36 }
  37
  38 int vsprintf(char *dst, char *fmt, va_list ap)
  39 {
  40         char *d = dst;
  41         char *s = fmt;
  42         while (*s) {
  43                 int c = *s++;
  44                 if (c != '%') {
  45                         *d++ = c;
  46                         continue;
  47                 }
  48                 switch ((c = *s++)) {
  49                 case 'd':
  50                         d = putint(d, va_arg(ap, long), 10, 1);
  51                         break;
  52                 case 'u':
  53                         d = putint(d, va_arg(ap, long), 10, 0);
  54                         break;
  55                 case 'x':
  56                         d = putint(d, va_arg(ap, long), 16, 0);
  57                         break;
  58                 case 's':
  59                         d = putstr(d, va_arg(ap, char *));
  60                         break;
  61                 case '\0':
  62                         s--;
  63                         break;
  64                 default:
  65                         *d++ = c;
  66                 }
  67         }
  68         *d = '\0';
  69         return d - dst;
  70 }
  71
  72 static char buf[1 << 12];
  73
  74 int printf(char *fmt, ...)
  75 {
  76         va_list ap;
  77         int ret;
  78         va_start(ap, fmt);
  79         ret = vsprintf(buf, fmt, ap);
  80         va_end(ap);
  81         return write(1, buf, ret);
  82 }
  83
  84 int sprintf(char *dst, char *fmt, ...)
  85 {
  86         va_list ap;
  87         int ret;
  88         va_start(ap, fmt);
  89         ret = vsprintf(dst, fmt, ap);
  90         va_end(ap);
  91         return ret;
  92 }