strlen,strcpy,strcat,strcmp,strstr,memcpy,的模拟实现方式

比眉伴天荒 2022-06-08 03:36 210阅读 0赞

#include<stdio.h>
    #include<stdlib.h>
    #include<Windows.h>
    #include<string.h>
    #include<assert.h>
    //模拟实现strlen三种实现方式
    int my_strlen_1(const char* str)
    {
        //使用计数器实现
        int count = 0;
        assert(str);
        while(*str)
        {
            count++;
            str++;
        }
        return count;
    }
    //第二种递归实现
    int my_strlen_2(const char* str)
    {
        assert(str);
        if(*str != '\0')
            return 1+my_strlen_2(str+1);
        else
            return 0;
    }
    //指针减指针模拟实现
    int my_strlen_3(const char* str)
    {
        const char *p = str;  
        while(*p)  
        {  
            p++;  
        }  
        return p-str;
    }
    int main()
    {
        int len1 = my_strlen_1("abcdef");
        int len2 = my_strlen_2("abcdef");
        int len3 = my_strlen_3("abcdef");
        printf("len1 = %d\n",len1);
        printf("len2 = %d\n",len2);
        printf("len3 = %d\n",len3);
        system("pause");
        return 0;
    }
    
    //模拟实现strcpy
    char* my_strcpy(char* dest,const char* src)
    {
        char *ret = dest;
        assert(src != NULL);
        assert(dest != NULL);
        while(*dest++ = *src++)
        {
            ;
        }
        return ret;
    }
    
    int main()
    {
        char arr[80]={
       0};
        printf("string=%s\n",my_strcpy(arr,"hello world"));
        system("pause");
        return 0;
    }
    //模拟实现strcat
    char *my_strcat(char *dest,char *src)
    {
        char *ret = dest;
        assert(dest);
        assert(src);
        while(*dest)
        {
            dest++;
        }
        while(*dest++ = *src++)
        {
            ;
        }
        return ret;
    }
    
    int main()
    {
        char arr1[15]="abcd";
        char *arr2="ef";
        printf("%s\n",my_strcat(arr1,arr2));
        system("pause");
        return 0;
    }
    //模拟实现strcmp
    int my_strcmp(const char* arr1,const char* arr2)
    {
      assert(arr1);
      assert(arr2);
      while(*arr1 == *arr2)
      {
       if(*arr1 == '\0')
         return 0;
       arr1++;
       arr2++;
      }
     return *arr1 - *arr2;
    }
    
    int main()
    {
     char *arr1="abcdef";
     char *arr2="abcd";
     int ret=my_strcmp(arr1,arr2);
     printf("%d\n",ret);
     system("pause");
     return 0;
    }
    
    //模拟实现strstr
    char* my_strstr(const char* str, const char* substr)  
    {  
        const char* s1 = str; 
        const char* s2 = substr;  
        const char* ret = str;//ret就是用来保存首地址的  
        assert(str);  
        assert(substr);
        if(strlen(s1)<strlen(s2))
            return NULL;
        while (*ret)  
        {  
            s1 = ret;s2 = substr;  
            while (*s1 && *s2 && (*s1 == *s2))  
            {  
                s1++;  
                s2++;  
            }  
            if (*s1 == '\0')  
            {  
                return NULL;  
            }  
            if(*s2 == '\0')
                return ret; 
            ret++;
        }  
        return NULL;  
    }  
    int main()  
    {  
        char a[20] = "abbbcdef";  
        char b[10] = "bbcde";  
        printf("%s\n", my_strstr(a, b));  
        system("pause");  
        return 0;  
    }  
    //模拟实现memcpy
    
    void* my_memcpy(void* dest, void* src,size_t n)  
    {  
        void* ret = dest;  
        char* str1 = (char*)dest;  
        char* str2 = (char*)src;  
        assert(dest);  
        assert(src);  
        while (n--)  
        {  
            *str1++ = *str2++;  
        }  
        return ret;  
    }  
    
    void* my_memmove(void* dest, void* src, size_t n)  
    {  
        void* ret = dest;  
        char* str1 = (char*)dest;  
        char* str2 = (char*)src;  
        assert(dest);  
        assert(src);  
        if (str1 > str2)   
        {  
            while (n--)  
            {  
                *(str1 + n) = *(str2 + n);  
            }  
        }  
        else  
        {  
            while (n--)  
            {  
                *str1++ = *str2++;  
            }  
        }  
        return ret;  
    }  
    
    int main()  
    {  
        int i = 0;  
        int arr1[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };  
        int arr2[10] = { 0 };  
        int arr3[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };  
        my_memcpy(arr2, arr1, sizeof(arr1));  
        my_memmove(arr3 + 5, arr3 + 4, 3 * sizeof(int));  
        for (i = 0; i < 10; i++)  
        {  
            printf("%d ", arr2[i]);  
        }  
        printf("\n");  
        for (i = 0; i < 10; i++)  
        {  
            printf("%d ", arr3[i]);  
        }  
        system("pause");  
        return 0;  
    }