Question

我在C ++中得到了这个警告。我猜想。

当我尝试使用g ++构建我的程序时

g++ --version

g++ (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4)
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

file.cpp: In function âvoid mainloop(THREAD_DATA*)â:
file.cpp:970: warning: statement has no effect

typedef
struct THREAD_DATA_
{
    struct spectate_player_t {
            bool        want_updates;   /* want player updates by specating all players every 100 milliseconds (who are in ship of course) */
            PLAYER  *last_spec_player;  /* last spectated player (just so it knows where it left off) */
            bool        direction; /* which direction spectating goes (used to avoid dead ends) so it cycles all players */ 
    } spectate[1];
} THREAD_DATA;

...

static void mainloop(THREAD_DATA *td)

第970行只是一个我曾经认为在C ++中一直工作的切换，所以它让我感到困惑，为什么它突然被删除或者警告没用？

Line 967: if(td->spectate->last_spec_player)
Line 968:    pkt_send_spectate_player(td->spectate->last_spec_player->pid);
Line 969: else
Line 970:    td->spectate->direction != td->spectate->direction;

Answer 1

它应该是：

td->spectate->direction = !td->spectate->direction;

由于!=是不等式运算符，a != a不等于a = !a，它等于!(a == a)

g ++（C ++）警告：语句无效（toggle bool！= bool）

1 个答案: