模拟实现strncpy,strncat,strncmp

//模拟实现strncat

//追加后添加’\0’

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <windows.h>
#include <assert.h>
char *my_strncat(char *des, const char *src, int count)
{
    assert(des);
    assert(src);
    char *cat = des;
    int i = ;
    while (*des != '\0')
    {
        des++;
    }
    for (; i <count; i++)
    {
        *des = *src;
        des++;
        *src++;
    }
    return cat;
}

int main()
{
    char a[] = {'a','b','c','\0'};
    char b[] = "world and bit";
    int n = ;
    char *ret = my_strncat(a, b, n);
    printf("ret: %s\n", ret);
    system("pause");
    return ;
}
           

模拟实现strncpy

//拷贝完后在后边追加’\0’

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <windows.h>
#include <assert.h>

char *my_strncpy(char *dst, const char *src, int n)
{
    assert(dst);
    assert(src);
    assert(n > );
    char *cpy = dst;
    while (n--)
    {
        *dst++ = *src++;
    }
    return cpy;

}

int main()
{
    char a[] = "abcdefgh";
    char *p = "1234";
    int n = ;
    char *ret = my_strncpy(a, p, );
    printf("ret: %s\n", ret);

    system("pause");
    return ;
}
           

模拟实现strncmp

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <windows.h>
#include <assert.h>

int my_strncmp(const char *str1, const char *str2, int n)
{
    assert(str1);
    assert(str2);
    assert(n > );
    const char *p = str1;
    const char *q = str2;
    while (*p != '\0' && *q != '\0' &&(n--))
    {

        if (*p ==*q)
        {
            p++;
            q++;

        }
        else if (*p > *q)
        {
            return ;
        }
        else 
        {
            return -;
        }

    }
    if (*p != '\0')
    {
        return ;

    }
    if (*q != '\0')
    {
        return -;
    }
}
int main()
{
    char *p = "abcd1234";
    char *q = "abcd2345";
    int n = ;
    int ret = my_strncmp(p, q, n);
    printf("ret = %d\n", ret);
    system("pause");
    return ;
}
           

以上！