从QString文档上弄过来的:
In all of the QString methods that take const char * parameters, the const char * is interpreted as a classic C-style '\0'-terminated string. It is legal for the const char * parameter to be 0.
简单的说就直接用,如果要修改QString(char *, 没有const),则需要strncpy,拷贝到其他缓冲区