How to pass a objective-c method to c function as callback?

Question

I've already read several articles about this question, but none of them solve my problem.

Briefly, in my NSApplicationDelegate, I called a function pcap_loop, pcap_loop needs a function pointer as callback, the callback signature is

void got_packet(u_char *, const struct pcap_pkthdr *, const u_char *)

I want to pass one of the NSApplicationDelegate's method as callback, so I can use these data in my app, somebody suggest me using "SEL + IMP", but I can't pass the self to callback, also somebody suggest "block", not work.

So, any idea?

Thanks!

Why do you need to use an Objective-C method for this? If it needs a C function, pass it a C function, period. You won't be able to do anything else in the lack of a self pointer. — user529758
– user529758, Commented Nov 19, 2012 at 8:15
@H2CO3 Is there anyway for me to get the NSApplicationDelegate instance in callback? I mean, something like [NSApplicationDelegate sharedInstance] — jiluo
– jiluo, Commented Nov 19, 2012 at 8:35
@MartinLuo In Cocoa : [[NSApplication sharedApplication] delegate], or [NSApp delegate]. And in iOS [[UIApplication sharedApplication] delegate] — Emmanuel
– Emmanuel, Commented Nov 19, 2012 at 10:09

Community · Accepted Answer · 2017-05-23 12:12:22Z

The essence of what you require can be found in this answer.

In your case you are calling pcap_loop:

int pcap_loop(pcap_t *p, int cnt, pcap_handler callback, u_char *user)

where pcap_handler is:

void got_packet(u_char *args, const struct pcap_pkthdr *header, const u_char *packet);

Now the last argument to pcap_loop, user, is passed as the first argument to got_packet, args and can be anything you wish. This corresponds to the argument cb_arg/anon in the previous answer. Now just follow the previous answer, passing a block which invokes your NSApplicationDelegate method as user and the C function to invoke that block as callback.

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