#include <stdio.h> #include <stdlib.h> #include <string.h> #include <assert.h> //memcpy：按字节复制 原型：extern void* memcpy(void *dest,void *src,unsigned int count) //功能：由src所指内存区域复制count个字节到dest所指的内存区域； //同strcpy void *memcpy_su(void *dest, void *src, unsigned int count) {        assert ((dest!=NULL)&&(src!=NULL));        char* bdest = (char*)dest;        char* bsrc = (char*) src;        while(count-->0)         *bdest++ = *bsrc++;        return dest; } //strcpy：复制字符串，遇到'\0'就结束 //原型：extern char *strcpy(char *dest,char *src) //功能：把src所指由'\0'结束的字符串复制到dest所指的数组中； //说明：src和dest所指内存区域是不可以重叠的且dest必须有足够的空间来容纳字符串。返回dest指针。 char *strcpy_su(char *dest,char *src) {        assert((dest!=NULL)&&(src!=NULL));        char *address = dest;        while((*dest++=*src++)!='\0')               continue;        return dest; } //memset：设置buffer所指的内存区域的前count个字节，用字符c来代替 //原型：extern void *memset(void *buffer,int c,int count);  void *memset_su(void *buffer, int c, int count) {    assert ((buffer!=NULL));    char* buffer2 = (char*)buffer;    while(count-->0)         *buffer2++ = c;        return buffer; } void main() {        char str1[100]="abchjhgjghjgjgh";        char str2[50]="efghdfkdjf";        strcpy(str1, str2);        printf("%s\n",str1);          char a[3];        memset(a, 'a', sizeof(a)-1);        memset(&a[2], '\0',1);        printf("%s\n",a);              memcpy(str1, str2, strlen(str2));        printf("%s\n",str1); }