How to pass a function pointer an argument in managed C++

yehiga1467

I am trying to call a function defined in the parent class via the object. But I am getting the error a pointer to member is not valid for a managed class. How can I achieve what I wanted? My expected output is to display the text "Called from child"

MyChild.h
ref class MyChild
{

   System:Void(\*my\_func\_ptr)(int, char\*);
   typedef System:Void(\*MyFuncPtrType)(int, char\*);
   MyFuncPtrType my\_func\_ptr;


public: MyChild ( System:Void(\*some\_func)(int, char\*)){

	my\_func\_ptr = some\_func;
}

public: System::Void  Child\_ButtonClicked(System::Object^ sender, System::EventArgs^ e){
	my\_func\_ptr();
}

}

MyForm.h

#include "MyChild.h"

public ref class MyForm : public System::Windows::Forms::Form
{
.
.
.
private: static System:Void test(int, char*) { //Update
MessageBox::Show("Called from child");
}

private: System::Void MyForm::MyForm\_Load(System::Object^ sender, System::EventArgs^ e) {
	MyChild^ child= gcnew MyChild( **MyForm::test**); **//type incompatible error in this line**
	child -> test(1,"random");
}

}

Update 2, Previous problem for //type incompatible error in this line is solved using the following way below.

MyChild.h
ref class MyChild
{

private:     System::Void(\*my\_func\_ptr)(int, char\*);

public:	System::Void doFunction(int A, char\* B) {
       (\*my\_func\_ptr)(A,B);
   }


public: MyChild ( System::Void(\*func)(int A, char\* B)){

	my\_func\_ptr = func;
}

public: System::Void  Child\_ButtonClicked(System::Object^ sender, System::EventArgs^ e){
	doFunction(1,"random");  //the arguments here are not used in later program, it is just for testing a function ptr with arguments
}

}

MyForm.h

#include "MyChild.h"

public ref class MyForm : public System::Windows::Forms::Form
{
.
.
.

   typedef System::Void (\*callback\_function)(int, char\*); 
   
   
private: static System:Void test(int, char\*) {
	MessageBox::Show("Called from child");
}


private: System::Void MyForm::MyForm\_Load(System::Object^ sender, System::EventArgs^ e) {


callback\_function disc;

disc = (callback\_function)(MyGUI::MyForm::test);

	MyChild^ child= gcnew MyChild( **disc**);
	child -> doFunction(1,"random");
}

}

For now, everything is solved but I am still unsure to the reason for incompatibility for argument and parameter having same type. I will do more trails and see if this is a stable

Lost User

In non-managed C/C++ you cannot use a pointer to a non-static member in that way. Make the test method to static, and it should work.

Richard Andrew x64

Look into the function Marshal.GetFunctionPointerForDelegate Method (System.Runtime.InteropServices) | Microsoft Docs[^]

The difficult we do right away... ...the impossible takes slightly longer.

yehiga1467

Hello, I have made to test() to static and now I have a new error at the same line that doesn't make sense to me. argument of type "void (*)(int, char*)" is incompatible with parameter of type "void (*)(int, char*)" Both the types are identical. I have also tried to change all types to void, and the error message is still the same i.e. argument of type "void (*)()" is incompatible with parameter of type "void (*)()" latest update: problem solved. Please see the first post! thanks!