C语言模拟实现strncpy、strncpy、strncat、strstr和strrstr函数实现

以下是我用C语言模拟实现的部分字符串函数：

1、strncpy函数的实现

#include<stdio.h>
#include<assert.h>
#include<iostream>
char*my_strncpy(char*dest, const char*src, int n)
{assert(dest != NULL);assert(src != NULL);int i = 0;char *tmp = dest;while ((i++<n)&&(*tmp++ = *src++ )!= '\0'){;}return dest;
}int main()
{char str1[] = "1234567890";char str2[] = "abcde";my_strncpy( str1,str2, 6);printf("%s\n", str1);system("pause");return 0;
}

2、strncmp函数的实现

#include<stdio.h>
#include<iostream>
#include<assert.h>
int my_strncmp(const char*str1, const char*str2,int n)
{assert(str1 != NULL);assert(str2 != NULL);while ((*str1!='\0')&&(*str2!='\0')&&n){if ((*str1 - *str2) > 0)return 1;if ((*str1-*str2)<0)return -1;str1++;str2++;n--;}if (*str1 == '\0'&&*str2 != '\0')return -1;if (*str1 != '\0'&&*str2 == '\0')return 1;return 0;
}
int main()
{char str1[] = "abcdef";char str2[] = "abcmln";int ret = my_strncmp(str1, str2,4);printf("%d\n", ret);system("pause");return 0;
}

3、strncat函数实现

#include<stdio.h>
#include<assert.h>
#include<iostream>
char*my_strncat(const char*src,char*dest, int n)
{assert(src != NULL&&dest != NULL);char*tmp = dest;while (*tmp != '\0'){tmp++;}while ((n--) && (*tmp++ = *src++) != '\0'){;}return dest;}
int main()
{char str1[20] = "hello ";char str2[6] = "word!";my_strncat(str2, str1, 2);printf("%s\n", str1);system("pause");return 0;
}

4、strstr函数的实现

#include<stdio.h>
#include<assert.h>
#include<string.h>
#include<iostream>
char*my_strstr(char*str1, char*str2)
{assert(str1 != NULL&&str2 != NULL);int i = 0;int j = 0;char*ret = 0;for (i = 0; str1[i] != 0; i++){for (j = 0; str2[j] != 0; j++){if (str1[i + j] != str2[j]){break;}}if (str2[j] == 0)return str1 + i;}return NULL;
}int main()
{char str[] = "abbcdbcdefmln";char str1[] = "bcd";//char *tmp=my_strstr(str, str1);printf("%s", my_strstr(str, str1));system("pause");return 0;
}

5、strrstr函数的实现

#include<stdio.h>
#include<assert.h>
#include<iostream>
char*my_strrstr(char*str1, char*str2)
{assert(str1 != NULL&&str2 != NULL);int i = 0;int j = 0;char*ret = 0;for (i = 0; str1[i] != 0; i++){for (j = 0; str2[j] != 0; j++){if (str1[i + j] != str2[j]){break;}}if (str2[j] == 0)ret=str1+i;}return ret;
}int main()
{char str[] = "abbcdbcdefmln";char str1[] = "bcd";//char *tmp=my_strstr(str, str1);printf("%s", my_strrstr(str, str1));system("pause");return 0;
}