I'm trapped in a situation of argument passing in libev.
Usually, libev receives packages in a function like *receive_callback*, that's OK, but in practice, we need to dispatch a relative *write_callback* to deal with specific jobs according to the received package. For example:
S_RECV_MSG* pstRecvMsg = (S_RECV_MSG*) recv_buff; switch(pstRecvMsg->wMsgType) { case 1: ev_io_init(w, write_callback1, w->fd, EV_WRITE); break; case 2: ev_io_init(w, write_callback2, w->fd, EV_WRITE); break; case 3: // ....... }
My question is, if the write_callbackX also has to read the specific content in the recv_buff, how can we pass the recv_buff argument to the callbackX? Must we bear the burden and ugliness of global variables here?
The author answered it himself, but in a comment. Since this shows up as unanswered, I am posting his answer in the "answer" section and closing the loop. Not sure if there is a better way... feel free to fix this.
Question author says:
Sorry, I think I got the answer now, and feel deeply ashamed at my carelessness of reading documentation:
struct my_io{ ev_io io; int otherfd; void *somedata; struct whatever *mostinteresting; }; // ... struct my_io w; ev_io_init (&w.io, my_cb, fd, EV_READ);
And then we use the my_io like this:
static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) { struct my_io *w = (struct my_io *)w_; //... }
Yes it's explained in libev document, and there is another way. Each watcher has a void *data member that you can read or modify, and libev will completely ignore it, so you can pass the argument like this:
w->data = (void *)recv_buff; ... static void my_cb (struct ev_loop *loop, ev_io *w_, int revents) { S_RECV_MSG *recv_buff = (S_RECV_MSG*)w_->data; ... }
see libev document.
翻译