FIX: new Allocates 0 Bytes for Typedef Class Function Pointer

View products that this article applies to.

This article was previously published under Q112985

SYMPTOMS

Using the new operator to dynamically allocate memory for a typedef pointer to a class member function that has return type void will allocate 0 (zero) bytes for the function pointer.

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STATUS

Microsoft has confirmed that this is a bug in the Microsoft products that are listed at the beginning of this article.

This problem was corrected in Microsoft Visual C++ .NET.

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When typecasting a pointer to a class member function that returns type void and trying to dynamically allocate pointers to this user defined type, the compiler allocates 0 (zero) bytes. This can best be seen by generating a mixed source/assembly language listing file using the /Fc compiler option and observing that the new operator is passed 0 bytes as the amount of memory to allocate. Using the sample code below, the following is the source/assembly listing for the call to new:

   ; 26   : // Try to allocate array of ptr's to ptr to member functions
   ; 27   : ppfVoid = new PtrVoid[10];  // Allocates zero bytes

     0002e     6a 00          push     0
     00030     e8 00 00 00 00     call     ??2@YAPAXI@Z   ; operator new

     00035     83 c4 04     add     esp, 4
     00038     89 45 fc     mov     DWORD PTR _ppfVoid$[ebp], eax

This problem occurs only when using a return type of void for the typedef pointer to class member function. Any other return type causes the proper amount of memory to be allocated by the new operator.

To work around this problem, allocate an array of chars using the sizeof() keyword to cause the new operator to allocate the proper number of bytes. The returned pointer will need to be typecast to the proper type.

The following code sample demonstrates the problem and workaround:

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Sample Code

   /* Compile options needed: /Fc
      To generate assembly/source listing */ 
   class CTest
   {
   public:
        void FcnVoid();
        int  FcnInt();
   };

   typedef void (CTest::*PtrVoid)(); // Defines PtrVoid as type pointer
                                     // to member function which returns
                                     // void.

   typedef int (CTest::*PtrInt)();   // Defines PtrInt as type pointer to
                                     // member function which returns int.

   void main(void)
   {
   PtrVoid *ppfVoid;  // Declares ppfVoid to be of type pointer to
                      // PtrVoid.
   PtrInt  *ppfInt;   // Declares ppfInt to be of type pointer to
                      // PtrInt.

   // Allocating ptr to ptr to member fcn that returns
   // int works correctly.

   ppfInt = new PtrInt;        // Allocates correct number of bytes.
   delete ppfInt;

   // Try to allocate array of ptr's to ptr to member functions.

   ppfVoid = new PtrVoid[10];  // Allocates 0 bytes.
   delete ppfVoid;

   // *** Use sizeof() to work around. ***
   // Allocate correct number of bytes and cast return
   // pointer to proper type.

   ppfVoid = (PtrVoid*)new char[sizeof(PtrVoid)*10];
   delete ppfVoid;
   }

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