C語言實現MyString

C語言實現strcpy strcat strstr strchr strcmp memcpy memove

char my_strcpy(char *dest, const char *src)//實現strcpy
{
    assert(dest);
    assert(src);
    while (*src)
    {
        *dest = *src;
        dest++;
        src++;
    }
    *dest = '\0';
}

int main()
{
    char dest[20] ="1234567890";
    char src []= "abcdef";
    my_strcpy(dest, src);
    printf("%s\n", dest);
    system("pause");
    return 0;
}

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

char my_strcat(char *dest, const char *src)//實現strcat
{
    assert(dest);
    assert(src);
    while (*dest != '\0')
    {
        dest++;
    }
    while (*src != '\0')
    {
        *dest = *src;
        dest++;
        src++;
    }
}
int main()
{
    char dest[20] = "1234567890";
    char src []= "abcdef";
    my_strcat(dest, src);
    printf("%s", dest);
    system("pause");
    return 0;
}

#include<stdio.h>
const char *Mystrchr(const char *src, char ch)//實現strchr
{
    while (*src != '\0')
    {
        if (*src == ch)
        {
            return src;
        }
        src++;
    }
    return NULL;
}
int main()
{
    char str[10] = "abcdefg";
    char a = 'b';
    printf("%s", Mystrchr(str,a));
    system("pause");
    return 0;
}

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

const char *My_strstr(const char *str1, const char *str2)實現strstr
{
    const char *s1 = NULL;
    const char *s2 = NULL;
    const char *start = str1;
    while (*start != '\0')
    {
        s1 = start;//s1回退到上一次的下一個位置
        s2 = str2;//s2回退到str2的起始位置
        while (*s1 != '\0' && *s2 != '\0'&&*s1 == *s2)
        {
            s1++;
            s2++;
        }
        if (*s1 == '\0')
        {
            return NULL;
        }
        if (*s2 == '\0')
        {
            return start;
        }
        start++;
    }
    return NULL;
}

int main()
{
    char dest[20] = "123aabcdef90";
    char src []= "abcdef";
    printf("%s\n", My_strstr(dest, src));
    system("pause");
    return 0;
}

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

int* my_strcmp(char *dest, const char *src)實現strcmp
{
    assert(dest);
    assert(src);
        while (*dest != '\0'&&*src!='\0')
        {
            if (*dest == *src)
            {
                dest++;
                src++;
            }
            else if (*dest > *src)
            {
                return 1;
            }
            else
            {
                return -1;
            }
        }
        return 0;
}
int main()
{
    char dest[] = "abcdef";
    char src []= "adcdef";
    int ret = my_strcmp(dest, src);
    printf("%d",ret);
    system("pause");
    return 0;
}

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

void* my_memcpy(void* dest, const void* src, size_t count)
{
    assert(src != nullptr&&dest != nullptr);
    //判斷dest指針和src指針是否爲空，若爲空拋出異常
    char* tmp_dest = (char*)dest;
    const char* tmp_src = (const char*)src;
    //將指針dest和指針src由void強轉爲char，
    //使得每次均是對內存中的一個字節進行拷貝
    while (count--)
        *tmp_dest++ = *tmp_src++;
    return dest;
}

int main()
{
    char dest[10];
    char* src="abc";
    if(sizeof(dest)<strlen(src)+1)
    {
        cout<<"dest空間不夠"<<endl;
        return 0;
    }
    else
        my_memcpy(dest,src,strlen(src)+1);
    return 0;
}

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

void* my_memmove(void* dest, const void* src, size_t count)
{
    assert(src != nullptr&&dest != nullptr);
    //判斷dest指針和src指針是否爲空，若爲空拋出異常
    char* tmp_dest = (char*)dest;
    const char* tmp_src = (const char*)src;

    if (tmp_src < tmp_dest)//當src地址小於dest地址時，從頭進行拷貝
        while (count--)
            *tmp_dest++ = *tmp_src++;
    else if (tmp_src > tmp_dest)//當src地址大於dest地址時，從後進行拷貝
    {
        tmp_src += count - 1;
        tmp_dest += count - 1;
        while (count--)
            *tmp_dest-- = *tmp_src--;
    }
    //else(tmp_src==tmp_dest) 此時不進行任何操做
    return dest;
}

int main()
{
    char dest[10];
    char* src="abc";
    if(sizeof(dest)<strlen(src)+1)
    {
        cout<<"dest空間不夠"<<endl;
        return 0;
    }
    else
        my_memmove(dest,src,strlen(src)+1);
    return 0;
}