libev 将参数传递给回调

Question

当我们调用 ev_io_init 时，我们给它一个具有 (struct ev_loop*, struct ev_io, int) 参数的函数地址，但是我们如何使参数像 (struct ev_loop*, struct ev_io, int, void *ptr) 并使 ev_io_init 用常量调用它ptr 值?

我知道如何携带来自 struct ev_io* 的额外数据，但我猜想为每个不同的事件保存相同的数据并不是一个好方法

Answer 1

来自the documentation：

ASSOCIATING CUSTOM DATA WITH A WATCHER

Each watcher has, by default, a void *data member that you can read or modify at any time: libev will completely ignore it. This can be used to associate arbitrary data with your watcher. If you need more data and don't want to allocate memory separately and store a pointer to it in that data member, you can also "subclass" the watcher type and provide your own data:
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 since your callback will be called with a pointer to the watcher, you can cast it back to your own type:
static void my_cb (struct ev_loop *loop, ev_io *w_, int revents)   
{
  struct my_io *w = (struct my_io *)w_;
  ...
}
More interesting and less C-conformant ways of casting your callback function type instead have been omitted.

既然你只想传递一个指针，最简单的方法肯定是把它放在data字段中。

libev 将参数传递给回调

libev pass argument to callback

c

io

libev

ASSOCIATING CUSTOM DATA WITH A WATCHER