callback problems

quote:

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Oluseyi how come this works:

int ( *Position::f )();
Position x;
f = x.abc();
f();

but not this:

int(*f)();

class is Position.

Position x;

(Position)(*f)()=x.abc();

just wondering.

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quote:

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Original post by Oluseyi

Alpha_ProgDes:
Because the signature of abc() is Position::abc(). Class members are different than non-class members (their calling convention is different - _thiscall vs _stdcall [C++] or _cdecl [C]).

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quote:

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Original Post by Fruny

C++ functions are ''cdecl'' just like C''s, Pascal''s (and Win32 API) are ''stdcall''. C++ only added the complication of name mangling. Of course, what you say is true of the member functions.

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void __stdcall CALLBACK vertexCallback(GLvoid *vertex)
{
	GLdouble *ptr;

	ptr = (GLdouble *) vertex;
	glVertex3dv((GLdouble *) ptr);
	glColor3dv((GLdouble *) ptr + 3);
}

int CTess::Init(GLvoid)
{
	// Create a new tessellation object 

	tobj = gluNewTess(); 

	// Set callback functions *** NOTE: i get errors on all 3 of these lines

	gluTessCallback(tobj, GLU_TESS_VERTEX, (GLvoid (*) ( )) &vertexCallback);
	gluTessCallback(tobj, GLU_TESS_BEGIN, (GLvoid (*) ( )) &glBegin);
	gluTessCallback(tobj, GLU_TESS_END, (GLvoid (*) ( )) &glEnd);

	return(1);
}
  

and the errors i get when trying to compile:
C:\CPP\LineTest\CTess.cpp(23) : error C2664: ''gluTessCallback'' : cannot convert parameter 3 from ''void (__cdecl *)(void)'' to ''void (__stdcall *)(void)''
        This conversion requires a reinterpret_cast, a C-style cast or function-style cast
C:\CPP\LineTest\CTess.cpp(24) : error C2664: ''gluTessCallback'' : cannot convert parameter 3 from ''void (__cdecl *)(void)'' to ''void (__stdcall *)(void)''
        This conversion requires a reinterpret_cast, a C-style cast or function-style cast
C:\CPP\LineTest\CTess.cpp(25) : error C2664: ''gluTessCallback'' : cannot convert parameter 3 from ''void (__cdecl *)(void)'' to ''void (__stdcall *)(void)''
        This conversion requires a reinterpret_cast, a C-style cast or function-style cast
Error executing cl.exe.
Creating browse info file...

TestBed.exe - 3 error(s), 0 warning(s)
 

''In C we had to code our own bugs. In C++ we can inherit them.''