fire event from C dll

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I created one dll using C programming language and visual studio, Its using in C#.net its working fine in my application. Now I need to fire an event from my C coded dll, How I can create an event in C coding and how I can call it from other language and my dll is not a COM component, I need to call one of the C# function from my c dll, I am using [DllImport(...)] to invoke c dll methods

Posted 16-Feb-12 23:20pm

Arun Kumar K S

Updated 17-Feb-12 19:46pm

v2

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bjorn_ht 17-Feb-12 6:12am

You should probably explain how you call your dll. Is it a plain C dll you load with [DllImport] attributes in the C# code, is it a managed C+ dll or something else?

2 solutions

Solution 1

It's not an event as such, but you can create a function in your C dll, that is called on initialization. One of its parameters is a pointer to a function.

In your C# code, you call that initialization function and hand over a delegate (may require some marshalling[^] knowledge). That delegate points to a function that fires your desired event.

In C, when you want the event to fire, you call the callback function you were given on initialization.

Posted 17-Feb-12 0:40am

lukeer

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Arun Kumar K S 18-Feb-12 1:13am

if possible please provide an exaple here is very helpful to me

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BobJanova · Accepted Answer · 2012-02-17T00:41:00

Solution 2

'Events' in the C world tend to be done through function pointers, i.e. you pass a function pointer to the function that starts a task, and it will be called when the task is complete.

// C declaration
extern int start_something(void (*f)()) { 
 // do some stuff ...
 (*f)(); // call back to the outside
}

Sometimes the function pointer is stored in a structure or registered with a single function and then used in response to others, but the idea is the same.

Through P/Invoke you can pass a delegate to functions with this type of signature, i.e.

[DllImport(...)]
public int start_something(VoidDelegate f);

public delegate void VoidDelegate();

(Apologies if I forgot how to write function pointers in C, it's been a long, long time :P.)

edit: updated C sample

Posted 17-Feb-12 0:41am

BobJanova

Updated 18-Feb-12 1:04am

v2

Comments

JackDingler 17-Feb-12 16:16pm

int (*start_something)(void*) = NULL;

BobJanova 17-Feb-12 16:22pm

start_something's supposed to be a (normal) function which _takes_ a pointer as a parameter, not itself a pointer.

JackDingler 17-Feb-12 16:44pm

Ahh, gotcha :)

You're right.

Arun Kumar K S 18-Feb-12 1:23am

if possible please provide an exaple here is very helpful to me

Arun Kumar K S 18-Feb-12 1:54am

I tried your its got some compiler error in int start_something((void*)() f) { ... }

Arun Kumar K S 18-Feb-12 1:58am

I got this following errors
Error 1 error C2059: syntax error : ')' d:\work\testcompilesflow\testeventinc\testlib\testlib\testevent.cpp 10 1 TestLib
Error 2 error C2143: syntax error : missing ';' before '{' d:\work\testcompilesflow\testeventinc\testlib\testlib\testevent.cpp 11 1 TestLib
Error 3 error C2447: '{' : missing function header (old-style formal list?) d:\work\testcompilesflow\testeventinc\testlib\testlib\testevent.cpp 11 1 TestLib
Error 4 error C3861: 'start_something': identifier not found d:\work\testcompilesflow\testeventinc\testlib\testlib\testevent.cpp 16 1 TestLib
5 IntelliSense: incomplete type is not allowed d:\work\testcompilesflow\testeventinc\testlib\testlib\testevent.cpp 10 29 TestLib
6 IntelliSense: expected an expression d:\work\testcompilesflow\testeventinc\testlib\testlib\testevent.cpp 10 53 TestLib
7 IntelliSense: expected a ')' d:\work\testcompilesflow\testeventinc\testlib\testlib\testevent.cpp 10 55 TestLib
8 IntelliSense: expected a ';' d:\work\testcompilesflow\testeventinc\testlib\testlib\testevent.cpp 11 2 TestLib

BobJanova 18-Feb-12 7:02am

You have to actually adapt what I've posted, not just post it verbatim and expect it to work, since it obviously has incomplete parts.

I did get the function pointer syntax wrong though (although you could have looked that up just as well as me).

extern int start_something(void (*f)()) {
// do some stuff ...
(*f)(); // call back to the outside
}