function pointer in c++ class throws compiler error

Question

I am new to function pointer and tried to pass the function pointer as parameter from one class to other and getting compiler error.

'fncptr1': is not a class or namespace name"

what am I doing wrong?

fncptr1.h

#ifndef FNCPTR1 #define FNCPTR1 #include "fncptr2.h" class fncptr1 { public: int addition(int a,int b); void testfncptr(); }; #endif // !FNCPTR1

fncptr1.cpp

 #include "fncptr1.h" #include <iostream> using namespace std; int fncptr1::addition(int a,int b) { return a + b; } void fncptr1::testfncptr() { fncptr2 f; f.implfncptr(&addition); }

fncptr2.h

 #ifndef FNCPTR2 #define FNCPTR2 #include "fncptr1.h" class fncptr2 { public: int implfncptr(int (fncptr1::*add)(int,int)); }; #endif // !FNCPTR2

fncptr2.cpp

 #include "stdafx.h" #include "fncptr2.h" #include <iostream> using namespace std; fncptr1 ff; int fncptr2::implfncptr(int (fncptr1::*add)(int, int)) { return (ff.*add)(1,2); }

main.cpp

fncptr1 f; f.testfncptr();

fncptr1.h includes fncptr2.h and fncptr2.h includes fncptr1.h, this is seriously wrong. — Jabberwocky
– Jabberwocky, Commented Aug 25, 2021 at 11:55
And f.implfncptr(&addition); should be f.implfncptr(&fncptr1::addition); — Ted Lyngmo
– Ted Lyngmo, Commented Aug 25, 2021 at 11:59
Also show main.cpp, the one you show is incomplete, and show the full error log. — Jabberwocky
– Jabberwocky, Commented Aug 25, 2021 at 12:00
It's also unclear what you're hoping for when calling f.testfncptr(); in main. The result of the addition is just thrown away. — Ted Lyngmo
– Ted Lyngmo, Commented Aug 25, 2021 at 12:04

Jabberwocky · Accepted Answer · 2021-08-25 12:20:19Z

Remove the includes of fncptr2.h and fncptr1.h from all .h files. Instead add them to fncptr1.c and fncptr2.c.
you need f.implfncptr(&fncptr1::addition); instead of f.implfncptr(&addition); in fncptr1.cpp

fncptr1.h

#ifndef FNCPTR1 #define FNCPTR1 class fncptr1 { public: int addition(int a, int b); void testfncptr(); }; #endif // !FNCPTR1

fncptr2.h

#ifndef FNCPTR2 #define FNCPTR2 class fncptr1; class fncptr2 { public: int implfncptr(int (fncptr1::* add)(int, int)); }; #endif // !FNCPTR2

fncptr1.cpp

#include "fncptr1.h" #include "fncptr2.h" #include <iostream> using namespace std; int fncptr1::addition(int a, int b) { return a + b; } void fncptr1::testfncptr() { fncptr2 f; f.implfncptr(&fncptr1::addition); }

fncptr2.cpp

#include "fncptr2.h" #include "fncptr1.h" #include <iostream> using namespace std; fncptr1 ff; int fncptr2::implfncptr(int (fncptr1::* add)(int, int)) { return (ff.*add)(1, 2); }

main.cpp

#include "fncptr1.h" int main() { fncptr1 f; f.testfncptr(); }

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