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Pointing to clasmen
I'VE Received a Lot of Questions Lately Such AS This About Pointers to Class Methods: "I Work with Visual C 4.0. I cannot USE The Pointer of a class method. The compiration error message is:
Cannot Convert Parameter 2 from 'long (unsigned long)' to 'long (__cdecl *) (unsigned long)' What shop i do? "
Here is The code for one way to solid this problem.
// in the header
Class Ckernel:
{
Long (* lpfunc) (DWORD);
Long Olesendtc (DWORD DWInfo);
}
// in the CPP file
Bool ckernel :: init ()
{
LPFUNC = OLESENDTC;
Return True;
}
Class methods all have one hidden argument, a pointer to the class object the method is called on. C uses this pointer to find the location of any class data that the method may reference. If you try and use a standard function pointer to call a Class Method, C Has No Way To Pass this Hidden Argument and a conflict results.
To help deal with this and to improve type safety, C added three new operators, :: *, *, and -.> *, To allow for safe pointers to members These pointers to members can point to either member functions or variables..
Class Ctest
{
PUBLIC:
BOOL init ();
Long Olesendtc (DWORD DWInfo);
}
Long (ctest :: * lpfunc) (DWORD DWINFO) = & ctest :: Olesendtc;
int main ()
{
CTEST TEST;
(TEST. * lpfunc) (0);
Return 0;
}
Long ctest :: OlesendTc (DWORD DWInfo)
{
COUT << "in Oleseendtc / N";
Return 0;
}
This example shows one use of pointers to members. The code uses the :: * operator to declare lpFunc as a pointer to a CTest member function. Note that, rather than assign a value to this pointer at run time, the pointer is simply initialized In the declaration.in the main function, this example uses the. * Operator to call the method Pointed to by lpfunc. if Test WERE A Pointer Here, You 10 Uses -> * Operator Instead.
C HAS a Lot of Things Going On Under The Hood Such AS Hidden Arguments to Methods. Pointers to Members Allow You to Safely Declare a Pointer To Safely Declare a Pointer To a class method and call method.
