JUST DO IT ~

目标缓冲区 小于 实际缓冲区

char *name = "1234567890";
char name2[6]={0};

memcpy_s( name2 ,  sizeof(name2) ,  name, strlen(name));

动态执行失败 (DEBUG ASSERTION FAILED !) 运行库和调试库都会提示出错.

注意:    指针sizeof( 指针 ) = 4  

strncpy(name2,name ,sizeof(name) );             打印name2  1234 

strncpy(name2,name ,strlen(name) );            打印name2   123456IOIPNUUY

优化这个语句,尽量拷贝内容

strncpy(name2,name ,   strlen(name)>sizeof(name2)? sizeof(name2): strlen(name)   );

目标缓冲区 小于 实际缓冲区

strncpy(name2,name ,sizeof(name2)-1 );

sizeof(name2)-1 ------------>让最后一个name2字符留给\0 否则这个字符也被拷贝了.

看一下LINUX下的两个函数的源代码，印象会更加深刻一些
void * memcpy(void * dest,const void *src,size_t count)
{
    char *tmp = (char *) dest, *s = (char *) src;
    while (count--)
        *tmp++ = *s++;
    return dest;
}
char * strcpy(char * dest,const char *src)
{
    char *tmp = dest;
    while ((*dest++ = *src++) != '\0')
        /* nothing */;
    return tmp;
}
老实讲，这两个函数长得是很帅

参考

http://stackoverflow.com/questions/4593907/difference-between-strncpy-and-memcpy

http://www.cppblog.com/Tim/archive/2011/04/02/143259.aspx