strncat()

将源字符串的前count个字符拷贝到目的字符串中

char *strncat(char *dest, const char *src, size_t count)
{
    assert((NULL != dest) && (NULL != dsrc));

    char *cp = dest;

    if (0 == count)//返回原来的
    {
        return dest;
    }

    while (*cp != '\0')
    {
        cp ++;
    }

    while (count-- > 0)
    {
        if (!(*cp++ = *src++))  //'\0'
        {
            return dest;
        }
    }

    *cp = '\0';

    return dest;
}