题目:就是实现位的替换
原型:void append(unsigned char *s,int n,unsigned char *buf,int len)
说明:s为目标字符串,n为位数,buf为缓冲区,len为buf的长度。
现在要在s中的第n位开始,赋上buf的值。
不能用动态内存分配函数。
求解答。
注意,我说的是位。。。。不是字节。。相当于是s中的第n位到第n+len位是buf的len位。
题目来自:http://topic.csdn.net/u/20111108/12/8eb961d4-7d35-4193-9ed4-ff3e71ca140e.html?85604
实现方法:
#include <stdio.h> void append(unsigned char *s,int n,unsigned char *buf,int len); void printa(unsigned char *a, int a_len); int main(int argc, char *argv[]) { unsigned char s[2] = {0x12,0x34}; unsigned char buf[2] = {0x45,0x56}; printa(s, sizeof(s)); printa(buf, sizeof(buf)); append(s, 2, buf, 3); printa(s, sizeof(s)); printa(buf, sizeof(buf)); return 0; } void append(unsigned char *s,int n,unsigned char *buf,int len) { unsigned char bits[8] = {0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01}; int i; for(i=0; i<len; ++i) { int x = i+n-1; if((*(buf+i/8)) & bits[i%8]) { *(s+x/8) |= bits[x%8]; } else { *(s+x/8) &= ~bits[x%8]; } } return; } void printa(unsigned char *a, int a_len) { int i; for(i=0; i<a_len; ++i) { printf("%02X ", a[i]); } printf("\n"); return; }