實現常用字符串函數的功能

在現在的Linux版本下，支持許多的API函數，平時我們用得是挺舒服的，但是我們不光要用API函數，更重要的是，我們要知道這些API函數是怎樣工作，執行的。我就用字符串的幾個重要的函數來舉例
一：字符串比較函數strcmp();

#include <stdio.h>    
#define MAX_SIZE 1024    

int my_strcmp(charchar *dest, charchar *src)    
{    

    charchar *temp = dest;    
    while(*src != '\0')    
    {    
        if(*temp > *src)    
        {    
            return 1;    
        }    
        else if(*temp < *src)    
        {    
            return -1;    
        }    
        temp++;    
        src++;    
    }    

    if(*src == '\0' && *temp == '\0')    
    {    
        return 0;    
    }    

    if(*src == '\0' && *temp != '\0')    
    {    
        return 1;    
    }    

    if(*temp == '\0' && *src != '\0')    
    {    
        return  -1;    
    }    
}    

int main()    
{    
    char src[MAX_SIZE] = "hello world a";    
    char dest[MAX_SIZE] = "hello world ";    

    int result = my_strcmp(dest,src);    

    printf("result = %d\n",result);    

    return 0;    
}  

二：字符串連接函數strcat();

#include <stdio.h>    

#define MAX_SIZE 1024    

charchar *my_strcat(charchar *dest, charchar *src)    
{    
    charchar *temp = dest;    
    while( *temp != '\0')    
    {    
        *temp++;    
    }    
    while(*src != '\0')    
    {    
        *temp = *src;    
        *temp++;    
        *src++;    
    }    
    *temp = '\0';    
    return dest;    
}    

int main()    
{    
    char src[MAX_SIZE] = "hi  where are yo doing";    
    char dest[MAX_SIZE] = "how are you";    

    charchar *temp = my_strcat(dest,src);    

    printf("temp = %s\n",temp);    
    printf("dest = %s\n",dest);    


    return 0;    
}    

三：字符串長度strlen();

#include <stdio.h>    
#include <string.h>    
#define MAX_SIZE 1024    

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

int main()    
{    
    char src[MAX_SIZE] = "hello world";    
    int len;    
    len = my_strlen(src);    

    printf("the len = %d\n",len);    

    return 0;    
}   

四：字符串拷貝函數strcpy();

#include <stdio.h>    
#include <string.h>    
#define MAX_SIZE     
charchar *my_strcpy(charchar *dest, charchar *src)    
{    
    charchar *temp = dest;    
    while(*src != '\0')    
    {    
        *temp = *src;    
        *temp++;    
        *src++;    
    }    
    *temp = '\0';    
    return dest;    
}    

int main()    
{    
    char src[MAX_SIZE] = "welcome to china";    
    char dest[MAX_SIZE] = "hello world";    

    charchar *temp = my_strcpy(dest,src);    

    printf("temp = %s\n",temp);    
    printf("dest = %s\n",dest);    

    return 0;    
}