Accessing function pointer inside class

Question

I am defining function pointer inside a class and trying to access it through an instance of the class but it shows an error.

Here is the code:

 1 #include<stdio.h>
 2 
 3 class pointer {
 4 public:
 5    int (pointer::*funcPtr)(int);
 6    pointer() {
 7       funcPtr = &pointer::check;
 8    }
 9 
10 
11    int check(int a)
12    {
13       return 0;
14    }
15 
16 };
17 
18 int main()
19 {
20    pointer *pt=new pointer;
21    return (pt->*funcPtr)(3);
22 }

It shows a compile time error:

checkPointer.cpp:21:15: error: ‘funcPtr’ was not declared in this scope

please help me.

Thank You in advance.

+1 Welcome to Stack Overflow! Thank you for providing a complete, concise testcase. See sscce.org for reasons why I wish everyone did that. — Robᵩ
– Robᵩ, Commented Mar 30, 2012 at 16:19

templatetypedef · Accepted Answer · 2012-03-30 15:37:47Z

2

The issue here is that funcPtr is declared inside of pt, so you need to use the name pt twice - once as the left-hand side of the pointer-to-member-selection, and once to choose the pointer class from which to select funcPtr:

(fn->*(fn->funcPtr))(3);

The reason for this is that you could potentially call the function pointed at by the funcPtr member of one instance of pointer on another instance of pointer.

Hope this helps!

answered Mar 30, 2012 at 15:37

templatetypedef

376k112 gold badges954 silver badges1.1k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

templatetypedef Over a year ago

@fschmitt- I don't believe so. funcPtr is the name of the data member of pt that I want to select. You don't need to use scope resolution to select a pointer-to-member-function.

user3458 · Accepted Answer · 2012-03-30 15:45:04Z

1

I think you meant

pt->*(pt->funcPtr)(3);

answered Mar 30, 2012 at 15:45

user3458

Comments

Robᵩ · Accepted Answer · 2012-03-30 16:18:24Z

1

I'm going to suggest that you follow the instructions from the C++ FAQ. Normally, that author avoids typedefs and #defines, but for this case he makes an exception:

#define CALL_MEMBER_FN(object,ptrToMember)  ((object).*(ptrToMember))
…
    CALL_MEMBER_FN(*pt, pt->funcPtr)(3)

P.s. Even if you don't follow those instructions, do read that page. It has loads of useful information about pointers to member functions.

answered Mar 30, 2012 at 16:18

Robᵩ

170k20 gold badges251 silver badges323 bronze badges

Collectives™ on Stack Overflow

Accessing function pointer inside class

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related