memccpy函数源码实现

最新推荐文章于 2021-05-19 15:10:21 发布

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本文介绍了如何实现一个自定义的memccpy函数，该函数用于从源src复制字节到目标dest，直到达到指定的计数count或遇到特定字符c。提供了两种不同写法的函数，详细解析了函数的内部逻辑，并通过main函数举例展示了函数的使用方法。

#include <stdlib.h> /* Copies bytes from src to dest until count bytes have been copied,or up to and including the character c, whichever comes first. 如果src前n个字节中存在’c’，返回指向字符’c’后的第一个字符的指针；否则返回NULL，src被复制。 */ void * my_memccpy(void *dest,constvoid *src,int c,int count) { while ( count && (*((char *)(dest = (char *)dest + 1) - 1) = *((char *)(src = (char *)src + 1) - 1)) != (char)c ) count--; return(count ? dest : NULL); } /*这个函数的while条件判断写的比较长，看的眼疼，等价与以下写法：*/ void * my_memccpy01(void *dst,constvoid *src,int c,int count) { while (count) { *(char *)dst = *(char *)src; dst = (char *)dst + 1; if(*(char *)src == (char) c) break; src = (char *)src + 1; count--; } return(count ? dst : NULL); } int main() { char a[12]; char * p; char * str ="ammana_babi"; char ch; ch = '9'; p = (char *)my_memccpy01(a,str,ch,strlen(str)+1); if(p == NULL) printf("/nCan't not find character. /n"); else { printf("/nFind the character! /n"); *p= '/0'; } printf("/nThe String which has been copied is:/t"); puts(a); printf("************************************"); ch = 'b'; p = (char *)my_memccpy01(a,str,ch,strlen(str)+1); if(p == NULL) printf("/nCan't not find character. /n"); else { printf("/nFind the character! /n"); *p = '/0'; } printf("/nThe String which has been copied is:/t"); puts(a); system("pause"); return 0; }