Cannot convert parameter problem

[Drew]

I have the following code in a header file (pseudocode):

template <class T>
class Pt3 : public Vec3<T>
{
public:
// Constructors
Pt3() {}

void setVertFcn( void (*vf)(T x, T y, T z)) { vertfcn = vf; }
}

and in another header:

class SplineCurve
{
public:
CurveD() { Pt3<double> pt; pt.setVertFcn( glVertex3d); }
}

Compiler complains:

error C2664: 'Pt3<T>::setVertFcn' : cannot convert parameter 1 from 'void
(GLdouble,GLdouble,GLdouble)' to 'void (__cdecl *)(T,T,T)'
with
[
T=double
]
and
[
T=double
]
This conversion requires a reinterpret_cast, a C-style cast or
function-style cast

So following the compilers suggestion:

SplineCurveD() { Pt3<double> pt; pt.setVertFcn( (void (__cdecl
*)(T,T,T))&glVertex3d); }

Error becomes:

error C2664: 'Pt3<T>::setVertFcn' : cannot convert parameter 1 from 'void
(__cdecl *)(T,T,T)' to 'void (__cdecl *)(T,T,T)'
with
[
T=double
]
and
[
T=double
]
This conversion requires a reinterpret_cast, a C-style cast or
function-style cast

What's the right way to do this cast?

Thanks,
Drew

 

[Drew]

I still receive a similar error:

CurveD() { Pt3<GLfloat> pt; pt.setVertFcn( &glVertex3d); }

error C2664: 'Pt3<T>::setVertFcn' : cannot convert parameter 1 from 'void
(__stdcall *)(GLdouble,GLdouble,GLdouble)' to 'void (__cdecl *)(T,T,T)'

It seems a calling convention problem. Can that even be cast or do I need
to change
my declaration? (void setVertFcn( void (*vf)(T x, T y, T z)) { vertfcn =
vf; })

Thanks,
Drew

 

[Guest]

__cdecl is the default calling convention, while __stdcall is used to call Win32 API functions. If you right click the project, select properties, select Advanced under the C++ node you can change it. I haven't tried, but by the look of it, functions that use it need a function prototype

You might be able to declare the function pointer as __stdcal

int (__stdcall *ptr)(int a, …)

But like I said, I haven't tried it

I've seen COM using it

class A : public ComThin

virtual HRESULT __stdcall QueryInterface(const IID& iid, void** ppv
â€


But I haven't tried that either

 

[Guest]

yes, you should change
void setVertFcn( void (*vf)(T x, T y, T z) ) { vertfcn = vff;
to
typedef void (*VF)(T x, T y, T z)
VF vertfcn
void setVertFcn( VF vff) { vertfcn = vff;

maybe the problem was that vertfcn was not properly declared in the example of your first post

 

[Drew]

Thanks! Using your suggestion plus casting the input arg in the
call fixed my problem.

Thanks again,
Drew