字符串拷贝函数的几种实现

#include "main.h"
//1, 此没有判断字符串的非空

/*
void scp(char de[], const char *sr)//用const修饰，表示不可修改
{
    int i;
    for(i = 0; i < strlen(sr); i++)
    {
     de[i] = *(sr + i);
    }
}*/

//2

/*
char *scp(char *dest, const char *src)//用const修饰，表示不可修改
{
    char *ret_string = dest;
    if((dest == NULL) || (src == NULL))
    {
        printf("arg wrong\n");
        return NULL;
    }
    while(*src !='\0')
    {
        *ret_string = *src;
        *ret_string++;
        src++;
    }
    *ret_string = '\0';
    return dest;
}*/
//3

char *scp(char *dest, const char *src)//用const修饰，表示不可修改
{
    char *ret_string = dest;
    if((dest == NULL) || (src == NULL))
    {
        printf("arg wrong\n");
        return NULL;
    }
    while(*src !='\0')
    {
        *dest = *src;
        dest++;
        src++;
    }
    *dest = '\0';
    return ret_string;
}

//4

/*
char *scp(char *dest, const char *src)//用const修饰，表示不可修改
{
    char *ret_string = dest;

    if((dest == NULL) || (src == NULL))
    {
        printf("arg wrong\n");
        return NULL;
    }
        while((*dest++ = *src++) != '\0');
     return ret_string;
}
*/