Visual Studio 'non-standard syntax; use '&' to create a pointer to member'

Question

I was trying to call a function with a function pointer where the function pointer is a class member.

I simplifed the code to only showcase the problem but the foo() function in the oiginal code is already writen so I cannot change it.

(In my actual code, foo is from GLFW (glfwSetKeyCallback) and A is an input handler class.)

The code is:

    #include <iostream>

    // this four line can not be changed
    typedef void(*fptr)(int);
    void foo(fptr f) {
        f(0);
    }

    void testOutA(int i) {
    }

    class A {
    public:
        void testInA(int i) {
        }
    };

    int main()
    {
        foo(testOutA); // works fine as it should be

        A * a = new A();

        foo(a->testInA); // ERROR

        return 0;
    }

The compilation error message is:

ERROR: error C3867: 'A::testInA': non-standard syntax; use '&' to create a pointer to member

Did you try using `&` to create a pointer to member, like the error says? — TartanLlama, Oct 20 '16 at 14:03
well I tryed to add & but I don't know where to add it so far I tryed the following ones but these where obviously wrong: &a->testInA, a->&testInA, &(a->testInA) — Sekkmer, Oct 20 '16 at 14:08
It won't work that way. What version of C++ do you have available? — nvoigt, Oct 20 '16 at 14:10

score 4 · Accepted Answer · edited May 23 '17 at 12:02

4

The type of the expression a->testInA is a pointer to a non-static member function.

It does not have the same type as fptr, so the compiler emits an error, albeit a cryptic one.

Compilation would pass if testInA were static.

See C++ function pointer (class member) to non-static member function for more details.

edited May 23 '17 at 12:02

Community

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answered Oct 20 '16 at 14:05

Bathsheba

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Visual Studio 'non-standard syntax; use '&' to create a pointer to member'

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