Lesson 22. Pattern 14. Overloaded functions

24.01.2012

When porting a 32-bit program to a 64-bit platform, you may encounter changes in its logic related to the use of overloaded functions. If a function is overlapped for 32-bit and 64-bit values, the access to it with an argument of a memsize-type will be translated into different calls on different systems. This technique may be useful as, for example, in this code:

static size_t GetBitCount(const unsigned __int32 &) {
  return 32;
}
static size_t GetBitCount(const unsigned __int64 &) {
  return 64;
}
size_t a;
size_t bitCount = GetBitCount(a);

But this change of logic is potentially dangerous. Imagine a program that uses a class to arrange the stack. This class is specific in that way that it allows you to store values of different types:

class MyStack {
...
public:
  void Push(__int32 &);
  void Push(__int64 &);
  void Pop(__int32 &);
  void Pop(__int64 &);
} stack;
ptrdiff_t value_1;
stack.Push(value_1);
...
int value_2;
stack.Pop(value_2);

A careless programmer saves into and then selects from the stack values of different types ("ptrdiff_t" and "int"). Their sizes coincide on the 32-bit system and everything is quite okay. But when the size of the type "ptrdiff_t" changes on the 64-bit system, the number of bytes saved into the stack gets larger than the number of bytes loaded then from the stack.

I think this type of errors is clear to you and you understand that one should be very careful about calls to overloaded functions when passing actual arguments of a memsize-type.

Diagnosis

PVS-Studio does not diagnose this pattern of 64-bit errors. First, it is explained by the fact that we have not encountered such an error in a real application yet, and second, diagnosis of such constructs involves some difficulties. Please write to us if you encounter such an error in real code.

The course authors: Andrey Karpov (karpov@viva64.com), Evgeniy Ryzhkov (evg@viva64.com).

The rightholder of the course "Lessons on development of 64-bit C/C++ applications" is OOO "Program Verification Systems". The company develops software in the sphere of source program code analysis. The company's site: http://www.viva64.com.

Contacts: e-mail: support@viva64.com, Tula, 300027, PO box 1800.