JUST DO IT ~

目標緩沖區 小于 實際緩沖區

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

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

動態執行失敗 (DEBUG ASSERTION FAILED !) 運行庫和調試庫都會提示出錯.

注意:    指針sizeof( 指針 ) = 4  

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

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

優化這個語句,盡量拷貝內容

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

目標緩沖區 小于 實際緩沖區

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

sizeof(name2)-1 ------------>讓最后一個name2字符留給\0 否則這個字符也被拷貝了.

看一下LINUX下的兩個函數的源代碼，印象會更加深刻一些
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;
}
老實講，這兩個函數長得是很帥

參考

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

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