strcpy,strcat,strstr,strcmp,memmove的实现

来源：互联网发布：mac可以装双系统吗编辑：程序博客网时间：2024/06/01 10:12

1.实现strcpy

把从src地址开始且含有'\0'结束符的字符串复制到以dest开始的地址空间

#include <stdio.h>#include <Windows.h>#include <assert.h>char* my_strcpy(char* dest, const char* src){assert(dest != NULL);assert(src != NULL);char* start = dest;while (*dest = *src){dest++;src++;}return start;}int main(){char arr1[] = "hello";char arr2[] = "world";my_strcpy(arr1, arr2);printf("%s\n", arr1);system("pause");return 0;}

2.strcat

用于连接两个字符串

#include <stdio.h>#include <assert.h>#include <Windows.h>char* my_strcat(char* dest, const char* src){assert(dest);assert(src);char* temp = dest;while (*dest)dest++;while (*dest++ = *src++){;}return temp;}int main(){char arr1[] = "hello ";char arr2[] = "world";my_strcat(arr1, arr2);printf("%s", arr1);system("pause");return 0;}

3.strstr

strstr(dest,src) 函数用于判断字符串src是否是dest的子串。如果是，则该函数返回src在dest中首次出现的地址；否则，返回NULL。

#include <stdio.h>#include <Windows.h>#include <assert.h>char* my_strstr(const char* dest, const char* src){assert(dest);assert(src);const char* cur = dest;while (*cur){const char* s1 = cur;const char* s2 = src;while ((*s1) && (*s2) && (*s1 == *s2)){s1++;s2++;}if (*s2 == '\0'){return (char*)cur;}cur++;}return NULL;}int main(){char arr1[] = "hello ";char arr2[] = "world";char* ret = my_strstr(arr1, "l");if (ret == NULL){printf("no\n");}else{printf("%s\n", ret);}system("pause");return 0;}

4.strcmp

strcmp用于比较两个字符串s1和s2，若s1>s2,返回1; s1==s2,返回0；若s1<s2,返回-1；

#include <stdio.h>#include <Windows.h>#include <assert.h>int my_strcmp(const char*s1, const char* s2){assert(s1);assert(s2);while (*s1 == *s2){if (*s1 == '\0')return 0;s1++;s2++;}if (*s1 > *s2)return 1;elsereturn -1;}int main(){char arr1[] = "hello ";char arr2[] = "world";int ret = my_strcmp(arr1, arr2);printf("%d\n", ret);system("pause");return 0;}

5.memmove

memmove用于从src拷贝count个字节到dest，如果目标区域和源区域有重叠的话，memmove能够保证源串在被覆盖之前将重叠区域的字节拷贝到目标区域中。但复制后src内容会被更改。但是当目标区域与源区域没有重叠则和memcpy函数功能相同。

#include <stdio.h>#include <Windows.h>#include <assert.h>void* my_memmove(const void* dest, const void* src,int count){assert(dest);assert(src);char* cur = (char*)dest;while (*cur){char* pdest = (char*)dest;char* psrc = (char*)src;if ((pdest > psrc) && (pdest < psrc + count)){while (count--)*(pdest+count) = *(psrc+count);}else{while (count--){*pdest = *psrc;}}cur++;}return dest;}int main(){int arr1[20] = { 1,2,3,4,5,6,7,8,9,0 };int arr2[10] = { 0 };my_memmove(arr1 + 3, arr1, 20);system("pause");return 0;}

如发现错误，请及时告知我谢谢~

1 0