Exception Handling and Resource Management

C++ exceptions present a significant challenge to memory and resource management. Normally, when you allocate memory on the heap (free store), you receive a pointer. When you are finished with that memory, you call delete() on the pointer and the memory is returned to the heap.

If your method throws an exception after the memory is allocated, but before the memory is restored, you will create a memory leak. The exception immediately exits the function and the pointer is never deleted. This greatly simplified example illustrates the issue:

#include <iostream.h>

class test
{
public:
   test():myVariable(5) 
   { 
      cout << "test constructor, allocating memory for "
                     "myVariable.\n"; 
      }
   ~test() 
   { 
      cout << "test destructor, memory restored!\n"; 
   }

private:
   int myVariable;
};

class myException
{
};

void SomeFunction();

int main()
{
   try
   {
      SomeFunction();
   }
   catch (...)
   {
      cout << "Caught exception! Not much I can do now to "
                     "clean up the memory.\n";
      return 0;
   }
   cout << "Completed SomeFunction.\n";
   return 0;
};

void SomeFunction()
{
   for (int i = 0; i < 5; i++)
   {
      test* pTest = new test; // create and initialize

      if (i == 4)
         throw new myException;

      delete pTest;
   }
}

The output from this code is as follows: