字符串操作函数

字符串操作函数的使用和模拟实现

#include<stdio.h>#include<assert.h>#include<string.h>//strcpy功能：把src所指由NULL结束的字符串复制到dest所指的数组中。'\0'也复制过去。char *my_strcpy(char *dest, const char *src)//模拟实现strcpy{char *tmp = dest;assert(dest != NULL);assert(src != NULL);while (*dest++ = *src++){;}return tmp;}//strstr功能：作用是找出str2字符串在str1字符串中第一次出现的位置（不比较结束符NULL)。char *my_strstr(char *str1, char *str2)//模拟实现strstr函数  {assert(str1);assert(str2);char *p1 = NULL;char *p2 = NULL;char *ptr = str1;while (*ptr){p1 = ptr;p2 = str2;while (*p1++ == *p2++){if (*p2 == '\0')return ptr;//此时ptr的首地址就是要查找的子字符串在的位置  }ptr++;//上面没找到，使ptr指向下一个位置继续寻找  }return NULL;}//strchr功能：查找字符串str中首次出现某个字符的位置char *my_strchr(char* str, char s)//模拟实现strchr{assert(str);while (*str != '\0'){if (*str == s)return str;str++;}return NULL;}//strcat功能：把src所指字符串添加到str结尾处(覆盖str结尾处的'\0')并添加'\0'。char *my_strcat(char* str, char* src)//模拟实现strcat{char *temp = str;assert(str);assert(src);while (*temp != '\0')temp++;while (*temp++ == *src++){;}return str;}//strcmp功能：比较字符串str1和str2。int my_strcmp(const char *str1,const char *str2){assert(str1);assert(str2);while (*str1 == *str2){if (*str1 == '\0')return 0;str1++;str2++;}return *str1 - *str2;}//strncpy功能：将字符串src中至多count个字符复制到字符串dest中。//如果字符串dest的长度小于count，其余部分用'\0'填补char *my_strncpy(char *dest, const char *src,int count)//模拟实现strncpy{char* temp = dest;assert(dest);assert(src);while (*src && count){*dest++ = *src++;count--;}if (count){while (count--)*dest = '\0';}return temp;}//strncat功能：将字符串src中至多count个字符连接到字符串dest中，追加空值结束符。返回处理完成的字符串。char* my_strncat(char* dest,const char* src, int count)//模拟实现strncat{char* ret = dest;assert(dest);assert(src);while (*dest != '\0')dest++;while (*dest++ == *src++ && count)count--;return ret;}//strncmt功能：比较字符串str1和str2中至多count个字符。//如果参数中任一字符串长度小于count, 那么当比较到第一个空值结束符时，就结束处理。int my_strncmp(char* str1, char* str2, int count)//模拟实现strncmp{assert(str1);assert(str2);while (*str1 == *str2 && --count){if (str1 == '\0')return 0;str1++; str2++;}return *str1 - *str2;}void StrcpyTest(){char src[] = "***";char dest[] = ".......";printf("strcpy:%s\n", strcpy(dest, src));printf("my_strcpy:%s\n", my_strcpy(dest, src));//******************************************char arr1[] = "abcdefg";char arr2[] = "cde";printf("strstr:%s\n", strstr(arr1, arr2));printf("my_strstr:%s\n", my_strstr(arr1, arr2));//******************************************char arr[] = "abcdefg";printf("strchr:%s\n", strchr(arr, 'c'));printf("my_strchr:%s\n", my_strchr(arr, 'c'));//******************************************char array1[10] = "****";char array2[] = "OOO";printf("strcat:%s\n", strcat(array1, array2));printf("my_strcat:%s\n", my_strcat(array1, array2));//*******************************************char str1[] = "hello";char str2[] = "world";printf("strcmp:%d\n", strcmp(str1, str2));printf("my_strcmp:%d\n", my_strcmp(str1, str2));//*******************************************char src1[] = "***";char dest1[] = ".......";printf("strncpy:%s\n", strncpy(dest1, src1, 2));printf("my_strncpy:%s\n", my_strncpy(dest1, src1, 2));//********************************************char string1[10] = "****";char string2[] = "OOO";printf("strncat:%s\n", strncat(string1, string2, 2));printf("my_strncat:%s\n", my_strncat(string1, string2, 2));//********************************************char s1[] = "hello";char s2[] = "helrld";printf("strncmp:%d\n", strncmp(s1, s2, 2));printf("my_strncmp:%d\n", my_strncmp(s1, s2, 2));}

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