⽤c语⾔中的putchar（）实现printf（）#include <stdio.h>
#include <stdlib.h>
#include<stdarg.h>
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
// ⽤putchar()实现printf()
static void
putch(int ch, int *cnt)
{
putchar(ch);
*cnt++;
}
int
vcprintf(const char *fmt, va_list ap)
{
int cnt = 0;
my_vprintfmt((void*)putch, &cnt, fmt, ap);
return cnt;
}
int
cprintf(const char *fmt, ...)
{
va_list ap;
int cnt;
va_start(ap, fmt);
cnt = vcprintf(fmt, ap);
va_end(ap);
return cnt;
}
int
strnlen(const char *s, size_t size)
{
int n;
for (n = 0; size > 0 && *s != '\0'; s++, size--)
n++;
return n;
}
enum {
// Kernel error codes -- keep in sync with list in
E_UNSPECIFIED    = 1,    // Unspecified or unknown problem
E_BAD_ENV    = 2,    // Environment doesn't exist or otherwise
// cannot be used in requested action
E_INVAL        = 3,    // Invalid parameter
E_NO_MEM    = 4,    // Request failed due to memory shortage
E_NO_FREE_ENV    = 5,    // Attempt to create a new environment beyond
/
/ the maximum allowed
E_FAULT        = 6,    // Memory fault
MAXERROR
};
/*
* Space or zero padding and a field width are supported for the numeric
* formats only.
*
* The special format %e takes an integer error code
* and prints a string describing the error.
* The integer may be positive or negative,
* so that -E_NO_MEM and E_NO_MEM are equivalent.
*/
static const char * const error_string[MAXERROR] =
{
[E_UNSPECIFIED]    = "unspecified error",
[E_BAD_ENV]    = "bad environment",
[E_INVAL]    = "invalid parameter",
[E_NO_MEM]    = "out of memory",
[E_NO_FREE_ENV]    = "out of environments",
[E_FAULT]    = "segmentation fault",
};
/
*
* Print a number (base <= 16) in reverse order,
* using specified putch function and associated pointer putdat.
*/
static void
printnum(void (*putch)(int, void*), void *putdat,
unsigned long long num, unsigned base, int width, int padc)
{
// first recursively print all preceding (more significant) digits
if (num >= base) {
printnum(putch, putdat, num / base, base, width - 1, padc);
} else {
// print any needed pad characters before first digit
while (--width > 0)
putch(padc, putdat);
}
// then print this (the least significant) digit
putch("0123456789abcdef"[num % base], putdat);
}
// Get an unsigned int of various possible sizes from a varargs list,
// depending on the lflag parameter.
static unsigned long long
getuint(va_list *ap, int lflag)
{
if (lflag >= 2)
return va_arg(*ap, unsigned long long);
else if (lflag)
return va_arg(*ap, unsigned long);
else
return va_arg(*ap, unsigned int);
}
// Same as getuint but signed - can't use getuint
// because of sign extension
static long long
getint(va_list *ap, int lflag)
{
if (lflag >= 2)
return va_arg(*ap, long long);
else if (lflag)
return va_arg(*ap, long);
else
return va_arg(*ap, int);
}
void
printfmt(void (*putch)(int, void*), void *putdat, const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
my_vprintfmt(putch, putdat, fmt, ap);
va_end(ap);
}
void
my_vprintfmt(void (*putch)(int, void*), void *putdat, const char *fmt, va_list ap) {
register const char *p;
register int ch, err;
unsigned long long num;
int base, lflag, width, precision, altflag;
char padc;
while (1) {
while ((ch = *(unsigned char *) fmt++) != '%') {
if (ch == '\0')
return;
putch(ch, putdat);
}
// Process a %-escape sequence
padc = '';
width = -1;
precision = -1;
lflag = 0;
altflag = 0;
reswitch:
switch (ch = *(unsigned char *) fmt++) {
// flag to pad on the right
case'-':
padc = '-';
goto reswitch;
// flag to pad with 0's instead of spaces
case'0':
padc = '0';
goto reswitch;
// width field
case'1':
case'2':
case'3':
case'4':
case'5':
case'6':
case'7':
case'8':
case'9':
for (precision = 0; ; ++fmt) {
precision = precision * 10 + ch - '0';
ch = *fmt;
if (ch < '0' || ch > '9')
break;
}
goto process_precision;
case'*':
precision = va_arg(ap, int);
goto process_precision;
case'.':
if (width < 0)
width = 0;
goto reswitch;
case'#':
altflag = 1;
goto reswitch;
process_precision:
if (width < 0)
width = precision, precision = -1;
goto reswitch;
// long flag (doubled for long long)
case'l':
lflag++;
goto reswitch;
c语言char的用法// character
case'c':
putch(va_arg(ap, int), putdat);
break;
// error message
case'e':
err = va_arg(ap, int);
if (err < 0)
err = -err;
if (err >= MAXERROR || (p = error_string[err]) == NULL)
printfmt(putch, putdat, "error %d", err);
else
printfmt(putch, putdat, "%s", p);
break;
// string
case's':
if ((p = va_arg(ap, char *)) == NULL)
p = "(null)";
if (width > 0 && padc != '-')
for (width -= strnlen(p, precision); width > 0; width--)
putch(padc, putdat);
for (; (ch = *p++) != '\0' && (precision < 0 || --precision >= 0); width--)
if (altflag && (ch < '' || ch > '~'))
putch('?', putdat);
else
putch(ch, putdat);
for (; width > 0; width--)
putch('', putdat);
break;
// (signed) decimal
case'd':
num = getint(&ap, lflag);
if ((long long) num < 0) {
putch('-', putdat);
num = -(long long) num;
}
base = 10;
goto number;
// unsigned decimal
case'u':
num = getuint(&ap, lflag);
base = 10;
goto number;
// (unsigned) octal
case'o':
// Replace this with your code.
putch('X', putdat);
putch('X', putdat);
putch('X', putdat);
break;
/
/ pointer
case'p':
putch('0', putdat);
putch('x', putdat);
num = (unsigned long long)
(uintptr_t) va_arg(ap, void *);
base = 16;
goto number;
// (unsigned) hexadecimal
case'x':
num = getuint(&ap, lflag);
base = 16;
number:
printnum(putch, putdat, num, base, width, padc);
break;
// escaped '%' character
case'%':
putch(ch, putdat);
break;
// unrecognized escape sequence - just print it literally default:
putch('%', putdat);
for (fmt--; fmt[-1] != '%'; fmt--)
/
* do nothing */;
break;
}
}
}
int main(int argc, char *argv[]) {
char s[]= "hello,world";
cprintf("6828 decimal is %o octal!\n", 6828);
cprintf("%s\n",s);
cprintf("%10s\n",s);
cprintf("%.10s\n",s);
cprintf("%-10s\n",s);
cprintf("%-015s\n",s);
cprintf("%0-15s\n",s);
cprintf("%015s\n",s);
cprintf("%15s\n",s);
cprintf("%.15s\n",s);
cprintf("%-15s\n",s);
cprintf("%15.10s\n",s);
cprintf("%-15.10s\n",s);
cprintf("%e\n",1);
cprintf("%e\n",2);
cprintf("%e\n",10);
cprintf("%s\n",0);
cprintf("x=%d y=%d\n", 3);
scanf("%*d"); return0;
}

版权声明：本站内容均来自互联网，仅供演示用，请勿用于商业和其他非法用途。如果侵犯了您的权益请与我们联系QQ:729038198，我们将在24小时内删除。