C語言--模擬庫函數strcpy,strcat,strcmp

C語言--模擬庫函數strcpy,strcat,strcmp

一、庫strcpy函數，把一個字符串復制到另外一個字符串中  

#include<stdio.h>
#include<assert.h>
char* my_srtcpy( char *srt, char*src)
{
    assert(srt);
    assert(src);
    char *tmp = src;
    while (*src++ = *srt++)
    {
        ;
    }
    return tmp;
}
int main(void)
{
    char* arr = "abcdef";
    char arr1[10];
    printf("%s\n",my_srtcpy(arr, arr1));
}

 

  二、庫strcat函數，把一個字符串追加到另一個字符串中  

#include<stdio.h>
#include<assert.h>
char* my_srtcat(char* srt,  const char* src)
{
    assert(srt!=NULL);
    assert(src!=NULL);
    char *ret = srt;
    while (*srt)
    {
        srt++;
    }
    while (*srt++ = *src++)
    {
        ;
    }
    return ret;
}
int main(void)
{
    char arr[15] = "abcdef";
    char* arr1 = "cd";
    printf("%s\n", my_srtcat(arr, arr1));
}

 

三、strcmp函數，比較兩個字符串str1，str2，相等返回0;str1>str2返回1；else 返回-1

#include<stdio.h>
#include<assert.h>
int my_srtcmp(const char*srt1, const char* srt2)
{
    assert(srt1);
    assert(srt2);
    while (*srt1 == *srt2)
    {
        if (*srt1 == '\0')
        {
            return 0;
        }
        srt1++;
        srt2++;    
    }
    if (srt1 > srt2)
    {
        return 1;
    }
    else
    {
        return -1;
    }
}
int main(void)
{
    char *arr = "abcd";
    char *arr1 = "abc";
    printf("%d\n", my_srtcmp(arr, arr1));
}