printf函数原型

typedef char *va_list;#define   _AUPBND        (sizeof (acpi_native_int) - 1)#define   _ADNBND        (sizeof (acpi_native_int) - 1)#define _bnd(X, bnd) (((sizeof (X)) + (bnd)) & (~(bnd)))#define va_arg(ap, T) (*(T *)(((ap) += (_bnd (T, _AUPBND))) - (_bnd (T,_ADNBND))))#define va_end(ap)    (void) 0#define va_start(ap, A) (void) ((ap) = (((char *) &(A)) + (_bnd (A,_AUPBND))))//start.cstatic char sprint_buf[1024];int printf(char *fmt, ...){va_list args;int n;va_start(args, fmt);n = vsprintf(sprint_buf, fmt, args);va_end(args);write(stdout, sprint_buf, n);return n;}int vsprintf(char *buf, const char *fmt, va_list args){  int len;  unsigned long num;  int i, base;  char *str;  char *s;  int flags;            // Flags to number()  int field_width;    // Width of output field  int precision;    // Min. # of digits for integers; max number of chars for from string  int qualifier;    // 'h', 'l', or 'L' for integer fields  for (str = buf; *fmt; fmt++)  {    if (*fmt != '%')    {      *str++ = *fmt;      continue;    }    // Process flags    flags = 0;repeat:    fmt++; // This also skips first '%'    switch (*fmt)    {      case '-': flags |= LEFT; goto repeat;      case '+': flags |= PLUS; goto repeat;      case ' ': flags |= SPACE; goto repeat;      case '#': flags |= SPECIAL; goto repeat;      case '0': flags |= ZEROPAD; goto repeat;    }    // Get field width    field_width = -1;    if (is_digit(*fmt))      field_width = skip_atoi(&fmt);    else if (*fmt == '*')    {      fmt++;      field_width = va_arg(args, int);      if (field_width < 0)      {    field_width = -field_width;    flags |= LEFT;      }    }    // Get the precision    precision = -1;    if (*fmt == '.')    {      ++fmt;         if (is_digit(*fmt))        precision = skip_atoi(&fmt);      else if (*fmt == '*')      {        ++fmt;        precision = va_arg(args, int);      }      if (precision < 0) precision = 0;    }    // Get the conversion qualifier    qualifier = -1;    if (*fmt == 'h' || *fmt == 'l' || *fmt == 'L')    {      qualifier = *fmt;      fmt++;    }    // Default base    base = 10;    switch (*fmt)    {      case 'c':    if (!(flags & LEFT)) while (--field_width > 0) *str++ = ' ';    *str++ = (unsigned char) va_arg(args, int);    while (--field_width > 0) *str++ = ' ';    continue;      case 's':    s = va_arg(args, char *);    if (!s)    s = "<NULL>";    len = strnlen(s, precision);    if (!(flags & LEFT)) while (len < field_width--) *str++ = ' ';    for (i = 0; i < len; ++i) *str++ = *s++;    while (len < field_width--) *str++ = ' ';    continue;      case 'p':    if (field_width == -1)    {      field_width = 2 * sizeof(void *);      flags |= ZEROPAD;    }    str = number(str, (unsigned long) va_arg(args, void *), 16, field_width, precision, flags);    continue;      case 'n':    if (qualifier == 'l')    {      long *ip = va_arg(args, long *);      *ip = (str - buf);    }    else    {      int *ip = va_arg(args, int *);      *ip = (str - buf);    }    continue;      case 'A':    flags |= LARGE;      case 'a':    if (qualifier == 'l')      str = eaddr(str, va_arg(args, unsigned char *), field_width, precision, flags);    else      str = iaddr(str, va_arg(args, unsigned char *), field_width, precision, flags);    continue;      // Integer number formats - set up the flags and "break"      case 'o':    base = 8;    break;      case 'X':    flags |= LARGE;      case 'x':    base = 16;    break;      case 'd':      case 'i':    flags |= SIGN;      case 'u':    break;      case 'E':      case 'G':      case 'e':      case 'f':      case 'g':        str = flt(str, va_arg(args, double), field_width, precision, *fmt, flags | SIGN);    continue;      default:    if (*fmt != '%') *str++ = '%';    if (*fmt)      *str++ = *fmt;    else      --fmt;    continue;    }    if (qualifier == 'l')      num = va_arg(args, unsigned long);    else if (qualifier == 'h')    {      if (flags & SIGN)    num = va_arg(args, short);      else    num = va_arg(args, unsigned short);    }    else if (flags & SIGN)      num = va_arg(args, int);    else      num = va_arg(args, unsigned int);    str = number(str, num, base, field_width, precision, flags);  }  *str = '/0';  return str - buf;}