这是linux中printf()的源码，不用完全看懂，大家应该多看看源码，感受一下大师编程的风格与思路，对于刚起步的童鞋有个良好的代码习惯，感兴趣的看一下吧。
/* -*- -*- ------------------------------------------------------- *
*
* Copyright (C) 1991, 1992 Linus Torvalds
* Copyright 2007 rPath, Inc. - All Rights Reserved
*
* This file is part of the Linux kernel, and is made available under
* the terms of the GNU General Public License version 2.
*
* ----------------------------------------------------------------------- */
/*
* Oh, it's a waste of space, but oh-so-yummy for debugging. This
* version of printf() does not include 64-bit support. "Live with
* it."
*
*/
#include "boot.h"
static int skip_atoi(const char **s)
{
int i = 0;
while (isdigit(**s))
i = i * 10 + *((*s)++) - '0';
return i;
}
#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 SMALL 32 /* Must be 32 == 0x20 */
#define SPECIAL 64 /* 0x */
#define __do_div(n, base) ({ \
int __res; \
__res = ((unsigned long) n) % (unsigned) base; \
n = ((unsigned long) n) / (unsigned) base; \
__res; })
static char *number(char *str, long num, int base, int size, int precision,
int type)
{
/* we are called with base 8, 10 or 16, only, thus don't need "G..." */
static const char digits[16] = "0123456789ABCDEF"; /* "GHIJKLMNOPQRSTUVWXYZ"; */
char tmp[66];
char c, sign, locase;
int i;
/* locase = 0 or 0x20. ORing digits or letters with 'locase'
* produces same digits or (maybe lowercased) letters */
locase = (type & SMALL);
if (type & LEFT)
type &= ~ZEROPAD;
if (base < 2 || base > 36)
return NULL;
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++] = (digits[__do_div(num, base)] | locase);
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++ = ('X' | locase);
}
}
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;
}
int vsprintf(char *buf, const char *fmt, va_list args)
{
int len;
unsigned long num;
int i, base;
char *str;
const 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 (isdigit(*fmt))
field_width = skip_atoi(&fmt);
else if (*fmt == '*') {
++fmt;
/* it's the next argument */
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 (isdigit(*fmt))
precision = skip_atoi(&fmt);
else if (*fmt == '*') {
++fmt;
/* it's the next argument */
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 *);
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 '%':
*str++ = '%';
continue;
/* integer number formats - set up the flags and "break" */
case 'o':
base = 8;
break;
case 'x':
flags |= SMALL;
case 'X':
base = 16;
break;
case 'd':
case 'i':
flags |= SIGN;
case 'u':
break;
default:
*str++ = '%';
if (*fmt)
*str++ = *fmt;
else
--fmt;
continue;
}
if (qualifier == 'l')
num = va_arg(args, unsigned long);
else if (qualifier == 'h') {
num = (unsigned short)va_arg(args, int);
if (flags & SIGN)
num = (short)num;
} 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 i;
va_start(args, fmt);
i = vsprintf(buf, fmt, args);
va_end(args);
return i;
}
int printf(const char *fmt, ...)
{
char printf_buf[1024];
va_list args;
int printed;
va_start(args, fmt);
printed = vsprintf(printf_buf, fmt, args);
va_end(args);
puts(printf_buf);
return printed;
} |
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