mysprintf函数，不断为操作系统开发加油（只是加入了二进制数的显示）

#include <stdio.h>

typedef char *va_list;

#define __va_rounded_size(TYPE) \
(((sizeof(TYPE)+sizeof(int)-1)/sizeof(int))*sizeof(int))
#define va_start(AP, LASTARG) \
(AP=((char *)&(LASTARG)+__va_rounded_size(LASTARG)))

#define va_end(AP) ((va_list)0)

#define va_arg(AP, TYPE) \
(AP+=__va_rounded_size(TYPE), \
*((TYPE *)(AP-__va_rounded_size(TYPE))))

int myprintf(char *buf, char *fmt, ...);
void itoa(int num, char *buf, unsigned int base);
unsigned int div(unsigned int *n, unsigned int b);

int main(void) {
	char buf[0x100];
	myprintf(buf, "%%%%%% %b %b %b %b %b %b %b %b ###", \
	128, 64, 32, 16, 8, 4, 2, 1);
	printf("%s\n", buf);
	myprintf(buf, "%%%%%% %b %b %b %b ###", \
	0x8000, 0x4000, 0x2000, 0x1000);
	printf("%s\n", buf);
	myprintf(buf, "%%%%%% %b %b %b %b ###", \
	0x800, 0x400, 0x200, 0x100);
	printf("%s\n", buf);
	return 1;
}


int myprintf(char *buf, char *fmt, ...) {
	va_list ap;
	va_start(ap, fmt);
	char buf1[64], *temp1;
	int d;
	char *s, c;
	while (*fmt) {
		if (*fmt == '%') {
			++fmt;
			switch (*fmt) {
			case '%':
				*buf++ = '%';
				fmt++;
				break;
			case 's':
				s = (char *)va_arg(ap, char *);
				while(*s)
					*buf++ = *s++;
				fmt++;
				break;
			case 'c':
				c = (char)va_arg(ap, char);
				*buf++ = c;
				fmt++;
		    	break;
			case 'd':
				d = (int)va_arg(ap, int);
				itoa(d, buf1, 10);
				temp1 = buf1;
				while (*temp1) {
					*buf++ = *temp1++;
				}
				fmt++;
				break;
			case 'x':
				d = (int)va_arg(ap, int);
				*buf++ = '0';
				*buf++ = 'x';
				itoa(d, buf1, 16);
				temp1 = buf1;
				while (*temp1) {
					*buf++ = *temp1++;
				}
				fmt++;
				break;
			case 'b':
				d = (int)va_arg(ap, int);
				itoa(d, buf1, 2);
				temp1 = buf1;
				while (*temp1) {
					*buf++ = *temp1++;
				}
				fmt++;
				*buf++ = 'b';
				break;
			}
		} else {
			*buf++ = *fmt++;
		}
	} 
	va_end(ap);
	*buf = '\0';
	return 1;
}

unsigned int div(unsigned int *n, unsigned int b) {
	int res;
	res = *n % b;
	*n = *n / b;
	return res;
}

void itoa(int num, char *buf, unsigned int base) {
	char digits[16] = "0123456789abcdef";
	char temp[64];
	int i = 0;
	while (num)
		*(temp + i++) = digits[div(&num, base)];
	while (i-- > 0)
		*buf++ = *(temp + i);
		*(buf) = '\0';
	return;
}