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Function Pointers

Started by SloppyJoe Dec 6, 2001 at 3:11 PM 3 replies 450+ views

Original Post

Dec 6, 2001 at 3:11 PM

After spending sometime trying to figure out pointers to functions I finally found out how they work. They are relatively simple. Suppose you had a function called DoSomething:

  
BOOL DoSomething(int nParameter)
{
     MessageBox(NULL, "This is a MessageBox", "Title", MB_OK);
     return(TRUE);
}

You would then make a pointer to a function like this:

  
//return_type (*var_name)(param_type)

BOOL (*lpfnDoSomething)(int);
(*lpfnDoSomething) = DoSomething;

And to call it:

  
(*lpfnDoSomething)(10);

That''s all.

SloppyJoe

NewDeal

Dec 6, 2001 at 3:23 PM

Thanks for sharing

EvilCrap

Dec 6, 2001 at 5:03 PM

yes, and casting looks like this:

long lfunc = (long)FUNCTIONADDRESS;
void (*pfunc)(int, int);
pfunc = (void(*)(int,int))lfunc;

invective

Dec 6, 2001 at 5:46 PM

Its a little easier to read if you typedef them so you don''t have to explicitly dereference the pointer everytime you make a call.

  
void print (void)
{
	std::cout << "hi\n";
}

void main( void )
{
	typedef void (*void_function_ptr) (void);
	void_function_ptr myPrint = print;
	myPrint ();
}

and don''t for get about the peculiarities of non static member functions (because of the implicit this parameter):
http://www.parashift.com/c++-faq-lite/pointers-to-members.html

LilBudyWizer

Dec 6, 2001 at 5:58 PM

Create a base class with your method declared as virtual. Create two or more classes derived off that base class that override or implement that method. Instantiate whichever is appropriate for the use needed, but store its pointer as a pointer to the base class. Then just call the method. That will call the function in the derived class for whichever class was actually instantiated. Polymorphism is your friend, learn it, use it.

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