查询va_list时找到的vsprintf函数的源代码，先记录下来，有时间再仔细研究下:
// vsprintf.c
//
// Print formatting routines
//
// Copyright (C) 2002 Michael Ringgaard. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
//
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
// 3. Neither the name of the project nor the names of its contributors
// may be used to endorse or promote products derived from this software
// without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.
//
#include
#include
#include
#ifdef KERNEL
#define NOFLOAT
#endif
#define ZEROPAD 1 // Pad with zero
#define SIGN 2 // Unsigned/signed long
#define PLUS 4 // Show plus
#define SPACE 8 // Space if plus
#define LEFT 16 // Left justified
#define SPECIAL 32 // 0x
#define LARGE 64 // Use 'ABCDEF' instead of 'abcdef'
#define is_digit(c) ((c) >= '0' && (c) <= '9')
static char *digits = "0123456789abcdefghijklmnopqrstuvwxyz";
static char *upper_digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
static size_t strnlen(const char *s, size_t count)
{
const char *sc;
for (sc = s; *sc != '\0' && count--; ++sc);
return sc - s;
}
static int skip_atoi(const char **s)
{
int i = 0;
while (is_digit(**s)) i = i*10 + *((*s)++) - '0';
return i;
}
static char *number(char *str, long num, int base, int size, int precision, int type)
{
char c, sign, tmp[66];
char *dig = digits;
int i;
if (type & LARGE) dig = upper_digits;
if (type & LEFT) type &= ~ZEROPAD;
if (base < 2 || base > 36) return 0;
c = (type & ZEROPAD) ? '0' : ' ';
sign = 0;
if (type & SIGN)
{
if (num < 0)
{
sign = '-';
num = -num;
size--;
}
else if (type & PLUS)
{
sign = '+';
size--;
}
else if (type & SPACE)
{
sign = ' ';
size--;
}
}
if (type & SPECIAL)
{
if (base == 16)
size -= 2;
else if (base == 8)
size--;
}
i = 0;
if (num == 0)
tmp[i++] = '0';
else
{
while (num != 0)
{
tmp[i++] = dig[((unsigned long) num) % (unsigned) base];
num = ((unsigned long) num) / (unsigned) base;
}
}
if (i > precision) precision = i;
size -= precision;
if (!(type & (ZEROPAD | LEFT))) while (size-- > 0) *str++ = ' ';
if (sign) *str++ = sign;
if (type & SPECIAL)
{
if (base == 8)
*str++ = '0';
else if (base == 16)
{
*str++ = '0';
*str++ = digits[33];
}
}
if (!(type & LEFT)) while (size-- > 0) *str++ = c;
while (i < precision--) *str++ = '0';
while (i-- > 0) *str++ = tmp[i];
while (size-- > 0) *str++ = ' ';
return str;
}
static char *eaddr(char *str, unsigned char *addr, int size, int precision, int type)
{
char tmp[24];
char *dig = digits;
int i, len;
if (type & LARGE) dig = upper_digits;
len = 0;
for (i = 0; i < 6; i++)
{
if (i != 0) tmp[len++] = ':';
tmp[len++] = dig[addr[i] >> 4];
tmp[len++] = dig[addr[i] & 0x0F];
}
if (!(type & LEFT)) while (len < size--) *str++ = ' ';
for (i = 0; i < len; ++i) *str++ = tmp[i];
while (len < size--) *str++ = ' ';
return str;
}
static char *iaddr(char *str, unsigned char *addr, int size, int precision, int type)
{
char tmp[24];
int i, n, len;
len = 0;
for (i = 0; i < 4; i++)
{
if (i != 0) tmp[len++] = '.';
n = addr[i];
if (n == 0)
tmp[len++] = digits[0];
else
{
if (n >= 100)
{
tmp[len++] = digits[n / 100];
n = n % 100;
tmp[len++] = digits[n / 10];
n = n % 10;
}
else if (n >= 10)
{
tmp[len++] = digits[n / 10];
n = n % 10;
}
tmp[len++] = digits[n];
}
}
if (!(type & LEFT)) while (len < size--) *str++ = ' ';
for (i = 0; i < len; ++i) *str++ = tmp[i];
while (len < size--) *str++ = ' ';
return str;
}
#ifndef NOFLOAT
char *ecvtbuf(double arg, int ndigits, int *decpt, int *sign, char *buf);
char *fcvtbuf(double arg, int ndigits, int *decpt, int *sign, char *buf);
static void cfltcvt(double value, char *buffer, char fmt, int precision)
{
int decpt, sign, exp, pos;
char *digits = NULL;
char cvtbuf[80];
int capexp = 0;
int magnitude;
if (fmt == 'G' || fmt == 'E')
{
capexp = 1;
fmt += 'a' - 'A';
}
if (fmt == 'g')
{
digits = ecvtbuf(value, precision, &decpt, &sign, cvtbuf);
magnitude = decpt - 1;
if (magnitude < -4 || magnitude > precision - 1)
{
fmt = 'e';
precision -= 1;
}
else
{
fmt = 'f';
precision -= decpt;
}
}
if (fmt == 'e')
{
digits = ecvtbuf(value, precision + 1, &decpt, &sign, cvtbuf);
if (sign) *buffer++ = '-';
*buffer++ = *digits;
if (precision > 0) *buffer++ = '.';
memcpy(buffer, digits + 1, precision);
buffer += precision;
*buffer++ = capexp ? 'E' : 'e';
if (decpt == 0)
{
if (value == 0.0)
exp = 0;
else
exp = -1;
}
else
exp = decpt - 1;
if (exp < 0)
{
*buffer++ = '-';
exp = -exp;
}
else
*buffer++ = '+';
buffer[2] = (exp % 10) + '0';
exp = exp / 10;
buffer[1] = (exp % 10) + '0';
exp = exp / 10;
buffer[0] = (exp % 10) + '0';
buffer += 3;
}
else if (fmt == 'f')
{
digits = fcvtbuf(value, precision, &decpt, &sign, cvtbuf);
if (sign) *buffer++ = '-';
if (*digits)
{
if (decpt <= 0)
{
*buffer++ = '0';
*buffer++ = '.';
for (pos = 0; pos < -decpt; pos++) *buffer++ = '0';
while (*digits) *buffer++ = *digits++;
}
else
{
pos = 0;
while (*digits)
{
if (pos++ == decpt) *buffer++ = '.';
*buffer++ = *digits++;
}
}
}
else
{
*buffer++ = '0';
if (precision > 0)
{
*buffer++ = '.';
for (pos = 0; pos < precision; pos++) *buffer++ = '0';
}
}
}
*buffer = '\0';
}
static void forcdecpt(char *buffer)
{
while (*buffer)
{
if (*buffer == '.') return;
if (*buffer == 'e' || *buffer == 'E') break;
buffer++;
}
if (*buffer)
{
int n = strlen(buffer);
while (n > 0)
{
buffer[n + 1] = buffer[n];
n--;
}
*buffer = '.';
}
else
{
*buffer++ = '.';
*buffer = '\0';
}
}
static void cropzeros(char *buffer)
{
char *stop;
while (*buffer && *buffer != '.') buffer++;
if (*buffer++)
{
while (*buffer && *buffer != 'e' && *buffer != 'E') buffer++;
stop = buffer--;
while (*buffer == '0') buffer--;
if (*buffer == '.') buffer--;
while (*++buffer = *stop++);
}
}
static char *flt(char *str, double num, int size, int precision, char fmt, int flags)
{
char tmp[80];
char c, sign;
int n, i;
// Left align means no zero padding
if (flags & LEFT) flags &= ~ZEROPAD;
// Determine padding and sign char
c = (flags & ZEROPAD) ? '0' : ' ';
sign = 0;
if (flags & SIGN)
{
if (num < 0.0)
{
sign = '-';
num = -num;
size--;
}
else if (flags & PLUS)
{
sign = '+';
size--;
}
else if (flags & SPACE)
{
sign = ' ';
size--;
}
}
// Compute the precision value
if (precision < 0)
precision = 6; // Default precision: 6
else if (precision == 0 && fmt == 'g')
precision = 1; // ANSI specified
// Convert floating point number to text
cfltcvt(num, tmp, fmt, precision);
// '#' and precision == 0 means force a decimal point
if ((flags & SPECIAL) && precision == 0) forcdecpt(tmp);
// 'g' format means crop zero unless '#' given
if (fmt == 'g' && !(flags & SPECIAL)) cropzeros(tmp);
n = strlen(tmp);
// Output number with alignment and padding
size -= n;
if (!(flags & (ZEROPAD | LEFT))) while (size-- > 0) *str++ = ' ';
if (sign) *str++ = sign;
if (!(flags & LEFT)) while (size-- > 0) *str++ = c;
for (i = 0; i < n; i++) *str++ = tmp[i];
while (size-- > 0) *str++ = ' ';
return str;
}
#endif
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 = "
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;
#ifndef NOFLOAT
case 'E':
case 'G':
case 'e':
case 'f':
case 'g':
str = flt(str, va_arg(args, double), field_width, precision, *fmt, flags | SIGN);
continue;
#endif
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;
}
int sprintf(char *buf, const char *fmt, ...)
{
va_list args;
int n;
va_start(args, fmt);
n = vsprintf(buf, fmt, args);
va_end(args);
return n;
}