模拟实现（c语言） 库函数strcat,strcmp,strcpy,srelen

分别模拟实现库函数
1.strcat
2.strcmp
3.strcpy
4.srelen

1.strcat

#include<stdio.h>
#include<string.h>

void Merge(char a[], char b[], int n)
{
    
    
    char* q = a;
    char* p = b;
    int m = 0;
    while (*q != '\0')
        q++;
    while (m <= n) {
    
    
        *q++ = *p++;
        m++;
    }
    puts(a);
}

int main()
{
    
    
    char a[100] = {
    
     0 };
    char b[100] = {
    
     0 };
    gets(a);
    gets(b);
    int n = strlen(b);
    Merge(a, b, n);
}

2.strcmp

#include <stdio.h>
#include <assert.h>

int Strcmp(const char* str1, const char* str2) {
    
    
    assert(str1 != NULL);
    assert(str2 != NULL);
    while (*str1 == *str2) {
    
    
        if (*str1 == '\0') {
    
    
            return 0;
        }
        ++str1;
        ++str2;
    }
    return *str1 - *str2;
}
int main() {
    
    
    char str1[] = "love";
    char str2[] = "move";
    int point = Strcmp(str1, str2);
    if (point == 0) {
    
    
        printf("str1 = str2\n");
    }
    else if (point > 0) {
    
    
        printf("str1 > str2\n");
    }
    else {
    
    
        printf("str1 < str2\n");
    }
    return 0;
}

3.strcpy

#include<stdio.h>
#include<string.h>

void my_strcpy(char *arr_1, char *arr_2)
{
    
    
    while (*arr_2!=0) {
    
    
        *arr_1++ = *arr_2++;
    }
}

int main()
{
    
    
    char arr_1[100] = {
    
     0 };
    char arr_2[100] = {
    
     0 };
    gets_s(arr_1);
    /*int a = strlen(arr_1);*/
    gets_s(arr_2);
    my_strcpy(arr_1, arr_2);
    printf("%s", arr_1);
}

4.srelen

#include<stdio.h>

void my_strlen(char* arr)
{
    
    
    int count = 0;
    while (*arr != 0) {
    
    
        arr++;
        count++;
    }
    printf("%d", count);
}

int main()
{
    
    
    char arr[100] = {
    
     0 };
    gets_s(arr);
    my_strlen(arr);
}