C++ : handle resources if constructors may throw exceptions (Reference to FAQ 17.4]

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There is a similar question here that covers what your asking.

In this case, if the call to new fails, then the memory for the pointer is guaranteed to be freed. If the call succeeds, and the constructor throws after that, you will have a memory leak.

The destructor of the class will not be called, because the object was never fully constructed. There are two ways to fix this.

1)

Have exceptions fully managed in the constructor:

class Foo
{
public:
    Foo()
    try
    {
        p = new p;

        throw /* something */; 
    }
    catch (...)
    {
       delete p;

       throw; //rethrow. no memory leak
    }
private:
    int *p;
};

2)

Or use a smart pointer. When a constructor is entered, all of its members have been constructed. And because when a constructor throws, and objects members have been constructed, they must be destructed. And a smart pointer fixes that:

class Foo
{
public:
    Foo() :
    p(new int)
    {
        throw /* something */; 
    }
private:
    std::auto_ptr<int> p;
};

More Related Contents:

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  2. If you shouldn’t throw exceptions in a destructor, how do you handle errors in it?
  3. Does C++ support ‘finally’ blocks? (And what’s this ‘RAII’ I keep hearing about?)
  4. C++ display stack trace on exception
  5. How can I propagate exceptions between threads?
  6. Throwing exceptions from constructors
  7. Why should exceptions be used conservatively?
  8. Should I use an exception specifier in C++?
  9. Why doesn’t C++ use std::nested_exception to allow throwing from destructor?
  10. How do exceptions work (behind the scenes) in c++
  11. Who deletes the memory allocated during a “new” operation which has exception in constructor?
  12. When and how should I use exception handling?
  13. Difference between C++03 throw() specifier C++11 noexcept
  14. C++: Safe to use longjmp and setjmp?
  15. In what ways do C++ exceptions slow down code when there are no exceptions thown?
  16. Catching exceptions from a constructor’s initializer list
  17. How much footprint does C++ exception handling add
  18. Will C++ exceptions safely propagate through C code?
  19. C++ – Arguments for Exceptions over Return Codes
  20. Exception Error c0000005 in VC++
  21. How is the C++ exception handling runtime implemented?
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  23. Throwing an exception from within a signal handler
  24. throw new std::exception vs throw std::exception
  25. What happens if a constructor throws an exception?
  26. Under what circumstances are C++ destructors not going to be called?
  27. Difference between a C++ exception and Structured Exception
  28. Measuring exception handling overhead in C++
  29. Why is a segmentation fault not recoverable?
  30. Throwing C++ exceptions across DLL boundaries

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