With a little help by stackoverflow: http://stackoverflow.com/questions/1485983/calling-c-class-methods-via-a-function-pointer
class Foo {
public:
void f() { std::cout << "hello world" << std::endl; }
};
int main()
{
Foo x;
void (Foo::*g)();
g = &Foo::f;
(x.*g)();
return 0;
}The problem is that a member function has an implicit "this" pointer as the first argument, to know what object to work with.
That's why assigning it to a void function pointer won't work.
Also, you need to keep the pointer to the object around, so you can pass it along when calling the callback later.
The C++11 way to solve it:
class Menu {
std::function<void()> onMenuClick;
};
class Foo {
void f();
};
Menu menu;
Foo x;
menu.onMenuClick = [&x] () { x.f() }; //using wrapper lambda
OR
menu.onMenuClick = std::bind(&Foo:f, &x); //using bind
the thing is i store a pointer to function in one struct
then in another struct i try to assign the function (from this structure)
struct TDropDownMenu
{
pt2Function MenuOnClick;
TDropDownMenu * Items;
};
struct TTERRA_TEX_OSD
{
void SetNoBlend()
{
some code here
}
TDropDownMenu menu;
void Init()
{
menu.Items[0].Items[0].MenuOnClick = &SetNoBlend();
}
Thats what i am trying to do.
EDIT.
i did what
Olof Hedman told to do.
after enabling c++11 support on android compiler it compiles, theres also lotta work to see if this works
but for now i thank you for support
now my code looks like this:
#include <functional>
struct TDropDownMenu
{
std::function<void()> MenuOnClick;
};
other header
struct TTERRA_TEX_OSD
{
void SetNoBlend() { brush_blend = 0; }
void Init()
{
BrushMenu.Items[3].Items[0].MenuOnClick = std::bind(&TTERRA_TEX_OSD::SetNoBlend, this);
}
};
I encountered a problem with:
std::function<void(int)> SpecialMenuOnClick;
LayerMenu.Items[3+i].Items[0].SpecialMenuOnClick = std::bind(&TTERRA_TEX_OSD::SelectLayer, this);
void SelectLayer(int index)
LayerMenu.Items[3+i].Items[0].SpecialMenuOnClick = std::bind(&TTERRA_TEX_OSD::SelectLayer, this, std::placeholders::_1);I would suggest against using std::bind, it has some caveats and it keeps getting worse and worse the more advanced usage you need for it. It is also particularly opaque to the compiler. It seems I'm not the only one. I mean seriously.
using std::bind gives me an error:
Just use a standard lambda. Is this what you're trying to do?
LayerMenu.Items[3+i].Items[0].SpecialMenuOnClick = [this]() { this->SelectLayer(); };
Thanks for those video links Krohm.
I thought about adding something about preferring lambdas, but I didn't have time to write it clearly... (but at least I wrote the lambda as the first option in my post)
Didn't know bind was _that_ bad though, now I have more arguments for always using wrapper lambdas.
LayerMenu.Items[3+i].Items[0].SpecialMenuOnClick = std::bind(&TTERRA_TEX_OSD::SelectLayer, this, std::placeholders::_1);compiles
but
LayerMenu.Items[3+i].Items[0].SpecialMenuOnClick = [this]() { this->SelectLayer(); };doesn't
can someone tell me why?
LayerMenu.Items[3+i].Items[0].SpecialMenuOnClick = [this](int index) { this->SelectLayer(index); };
