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caelestis

Member

Registered: 2009-04-04

Posts: 88

g++ problem

The following code works fine with VC express, but not in GCC. Does anyone know why it won't compile? It gives this error:

conversion from 'main()::functor' to non-scalar type 'std::tr1::function<void()>' requested

Same thing happens if I use boost::function instead of std::tr1::function.

#include <iostream>
#include <tr1/functional>
#include <tr1/functional_hash.h>

void callfunc(std::tr1::function<void()> func) {func();}

int main() {
    struct functor {
        void operator()(void) {std::cout << "lol" << std::endl;}
    };
    functor f;
    callfunc(f);
}

sr

Member

Registered: 2009-10-12

Posts: 51

Re: g++ problem

I don't know the internals of tr1::function, but it seems to me that g++ is complaining about a valid failed type conversion.

Could you try declaring functor as:

struct functor: public std::tr1::function<void()> {

caelestis

Member

Registered: 2009-04-04

Posts: 88

Re: g++ problem

You suggested:

#include <iostream>
#include <tr1/functional>
#include <tr1/functional_hash.h>

using std::tr1::function;

void callfunc(function<void()> func) {func();}

int main() {
    struct functor : public function<void()>  {
        void operator()(void) {std::cout << "lol" << std::endl;}
    };
    functor f;
    callfunc(f);
}

This happens:

terminate called after throwing an instance of 'std::tr1::bad_function_call'  what(): std::exception

sr

Member

Registered: 2009-10-12

Posts: 51

Re: g++ problem

Ah, well it was just the simplest way of avoiding that particular error, short of an explicit cast, which I assumed wouldn't work either.

Edit: could you try moving the struct declaration out of main, instead? I believe gcc's local class declarations are causing the problem here, since according to tr1, your syntax appears perfectly correct.

Last edited by sr (2009-10-13 04:47:17)

sr

Member

Registered: 2009-10-12

Posts: 51

Re: g++ problem

Just to be clear, this works for me:

#include <iostream>
#include <tr1/functional>

void callfunc(std::tr1::function<void()> &func) {func();}

struct functor{
    void operator()() {std::cout << "lol" << std::endl;}
};

int main(int, char*[]) {

    std::tr1::function<void()> f = functor();
    callfunc(f);
}

Moving the struct into main() doesn't, for some reason - at least, I *think* I understand why it doesn't, but don't see why it works that way.

caelestis

Member

Registered: 2009-04-04

Posts: 88

Re: g++ problem

Nvm, gcc doesn't support it yet.

http://gcc.gnu.org/gcc-4.4/cxx0x_status.html