// test04funktionzeiger.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <iostream>
using namespace std;
int test(int a, int (*func)(int))
{
std::cout << (*func)(a);
return 0;
}
int sum(int i)
{
return i+i;
}
class Foo
{
public:
double One( long inVal ){return inVal;}
double Two( long inVal ){return inVal;}
double Three( double (Foo::*f)(long) )
{
return (*f)(1); // <--- why does this not work?
// coumpiler output:
// error C2171: '*' : illegal on operands of type 'double (__thiscall Foo::* )(long)'
// error C2064: term does not evaluate to a function taking 1 arguments
}
};
int main( int argc, char **argv )
{
double (Foo::*funcPtr)( long ) = &Foo::One;
Foo aFoo;
double result =(aFoo.*funcPtr)( 2 );
aFoo.Three(&Foo::Two);
test(2,&sum);
return 0;
}
Help on function pointers plz :)
Author
Y'know, I didn't really pay attention to the pointer's lessons that I find on the internet.. :) Have you tried removing the '*'? If that doesn't work, I can't help you. It looks like your casting the 'f'.
If I remember well (been a long time since C), I think you should do this
return f(1); and not return (*f)(1)
return f(1); and not return (*f)(1)
Author
Quote:Original post by Ali_BIf i change it that way this is the not working result:
If I remember well (been a long time since C), I think you should do this
return f(1); and not return (*f)(1)
#include "stdafx.h"#include <iostream>using namespace std;int test(int a, int (*func)(int)){ std::cout << (*func)(a); return 0;}int sum(int i){ return i+i;}class Foo{public: double One( long inVal ){return inVal;} double Two( long inVal ){return inVal;} double Three( double (Foo::*f)(long) ) { return f(1); // <--- why does this not work? // coumpiler output: // C2064: term does not evaluate to a function taking 1 arguments }};int main( int argc, char **argv ){ double (Foo::*funcPtr)( long ) = &Foo::One; Foo aFoo; double result =(aFoo.*funcPtr)( 2 ); aFoo.Three(&Foo::Two); test(2,&sum); return 0;}
In order to call function pointers to member functions, you have to invoke some strange arcane sytax, which in your case will look something like this:
return (this->*f)(1);
return (this->*f)(1);
Author
AFAIK the topic should be callback functions in c++ or something like that.
With a static class everything works as expected.
Thanks Sandman now i can sleep better again. As far as i remember x->y translates into (*x).y:
But if you try to write it that way in that callback fuction pointer case the compiler refuses to take it.
Indeed arcane.
[Edited by - Jonus on July 18, 2005 10:45:20 AM]
#include "stdafx.h"#include <iostream>using namespace std;int test(int a, int (*func)(int)){ std::cout << (*func)(a); return 0;}int sum(int i){ return i+i;}class Foo{public: double One( long inVal ){return inVal;} double Two( long inVal ){return inVal;} double Three( double (Foo::*f)(long) ) { return (this->*f)(1); // <--- Ha, Sandman you saved the day!!! I own you one. }};class Foo2{public: static double One( long inVal ){return inVal;} static double Two( long inVal ){return inVal;} static double Three( double (*f)(long) ) { return (*f)(3); // <--- works! }};int main( int argc, char **argv ){ // test for foo (instanced class) double (Foo::*funcPtr)( long ) = &Foo::One; Foo aFoo; double result =(aFoo.*funcPtr)( 2 ); aFoo.Three(&Foo::Two); // test for foo2 (static class) double (*funcPtr2)( long ) = &Foo2::One; double result2 =(*funcPtr2)( 2 ); Foo2::Three(&Foo2::Two); // test for global function test(2,& sum); return 0;}Thanks Sandman now i can sleep better again. As far as i remember x->y translates into (*x).y:
#include <iostream>class test{public: void a(){std::cout << "test!" << std::endl;};};int _tmain(int argc, _TCHAR* argv[]){ test * a = new test; a->a(); (*a).a(); delete a; return 0;}But if you try to write it that way in that callback fuction pointer case the compiler refuses to take it.
Indeed arcane.
[Edited by - Jonus on July 18, 2005 10:45:20 AM]
This topic is closed to new replies.
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