Day28~实现strlen、strcpy、strncpy、strcat、strncat

实现strlen、strcpy、strncpy、strcat、strncat

#include <stdio.h>

size_t my_strlen(const char *src)
{
    size_t len = 0;

    while (*src != '\0')
    {
        len++;
        src++;
    }
    return len;
}

char *my_strcpy(char *dest, const char *src)
{
    if (dest == NULL || src == NULL) // 判断输入的字符是否为空
    {
        return NULL; // 如果为空，就返回空
    }

    char *temp = dest; // 将dest的地址赋值给一个临时变量

    while (*src != '\0') // 遍历要拷贝的字符
    {
        *temp = *src; // 将src的值赋给temp
        src++;        // src地址后移
        temp++;       // temp地址后移
    }

    *temp = '\0'; // 最后一位为\0
 
    return dest; // 返回dest
}

char *my_strncpy(char *dest, const char *src, size_t n)
{
    if (dest == NULL || src == NULL)
    {
        return NULL;
    }

    char *temp = dest;

    size_t i;

    for (i = 0; (i < n) && (*src != '\0'); i++)
    {
        *temp = *src;
        src++;
        temp++;
    }

    for (; i < n; i++)
    {
        *temp = '\0';
    }

    return dest;
}

char *my_strcat(char *dest, const char *src)
{
    if (dest == NULL || src == NULL)
    {
        return NULL;
    }

    char *temp = dest;

    while (*temp != '\0')
    {
        temp++;
    }

    while (*src != '\0')
    {
        *temp = *src;
        temp++;
        src++;
    }

    *temp = '\0';

    return dest;
}

char *my_strncat(char *dest, const char *src, size_t n)
{
    if (dest == NULL || src == NULL)
    {
        return NULL;
    }

    char *temp = dest;

    while (*temp != '\0')
    {
        temp++;
    }

    size_t i;

    for (i = 0; (i < n) && (*src != '\0'); i++)
    {
        *temp = *src;
        src++;
        temp++;
    }

    for (; i < n; i++)
    {
        *temp = '\0';
    }

    return dest;
}

int main()
{
    char dest[100] = "Hello World";
    char src[100] = "Hello World";

    // char *result1 = my_strcpy(dest, src);
    // char *result2 = my_strncpy(dest, src, 3);
    // size_t result = my_strlen(src);
    // char *result3 = my_strcat(dest, src);
    char *result4 = my_strncat(dest, src, 3);

    // printf("%s\n", result1);
    // printf("%s\n", result2);
    // printf("%ld\n", result);
    // printf("%s\n", result3);
    printf("%s\n", result4);

    return 0;
}