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How to call a class member function via function pointer in map [C++]

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How to call a class member function via function pointer in map [C++]

 
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  #1
Jul 6th, 2009
I'm trying to declare a std::map that is keyed by a char and has a function pointer as a second parameter, these functions would be a member function of my class. But for some odd reason I cannot call the functions when extracted...

So, I have a class A as shown below, it contains a map as well as a function

C++ Syntax (Toggle Plain Text) 
  1. class A
  2. {
  3. private:
  4. 	map<char, void (A::*)(void)> mapA;
  5. public:
  6. 	void func();

Next I have main code that looks like this:
C++ Syntax (Toggle Plain Text) 
  1. A::A()	// constructor
  2. {
  3. 	// Generate User Options
  4. 	mapA['a'] = &A::func;
  5. }

Now, I try to execute func by extracting it from the map and running the function:
C++ Syntax (Toggle Plain Text) 
  1. 	map<char, void (A::*)(void)>::iterator it;
  2. 	for ( it=mapA.begin() ; it != mapA.end(); it++ )
  3. 	{
  4. 		(*it).second();
  5. 	}

I would assume this would launch function "func" as it is stored in the map, but instead it generates the following error message:
error C2064: term does not evaluate to a function taking 0 arguments

Any help would be greatly appreciated...
Thanks,
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Re: How to call a class member function via function pointer in map [C++]

 
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  #2
Jul 6th, 2009
It works with static method only.
Last edited by adatapost; Jul 6th, 2009 at 4:06 am.
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Re: How to call a class member function via function pointer in map [C++]

 
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  #3
Jul 6th, 2009
Try boost::function -> http://www.boost.org/doc/libs/1_39_0.../function.html
Last edited by jencas; Jul 6th, 2009 at 5:13 am. Reason: link added
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Re: How to call a class member function via function pointer in map [C++]

 
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  #4
Jul 6th, 2009
try the following.

the syntax seems difficult but look it carefully.
C++ Syntax (Toggle Plain Text) 
  1. (f.*((*it).second))();
  2. (f.*(it->second))();

the easier way is to create the typedef and assign the return value of m['a'] to that, and then call that pointer to member function.

like below.
C++ Syntax (Toggle Plain Text) 
  1. typedef void (A::*FMemPtr)(void);
  2.  
  3. map<char, FMemPtr> m;
  4. m['a'] = &A::func;
  5.  
  6. FMemPtr funcPtr = m['a'];
  7. A obj;
  8. (obj.*funcPtr)();
same goes for iterator.

hope this helps
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Re: How to call a class member function via function pointer in map [C++]

 
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  #5
Jul 6th, 2009
by the way following is also a legal syntax.
C++ Syntax (Toggle Plain Text) 
  1. (obj.*m['a'])();

.
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