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(C++) boost::scoped_ptr

 

boost::scoped_ptr is a smart pointer that deletes the instance it points to when going out of scope.

 

boost::scoped_ptr is similar to std::auto_ptr, except that you cannot copy a boost::scoped_ptr (when you do this with std::auto_ptr, you might get behaviour you did not expected).

 

#include <boost/scoped_ptr.hpp>

int main()
{
  const boost::scoped_ptr<MyClass> p(new MyClass);
  p->doStuff(); //Hey, the same way of accessing the pointed instance!
  //Done, boost::scoped_ptr deletes itself when going out of scope
}

 

 

 

 

 

Boost Smart pointers and null

 

Boost smart pointers check for null themselves, so there is no need to check these to be inititialized. In the example below a member variable of a class is requested from an unitialized smart pointer. The program will abort and the runtime error will be shown.

 

#include <boost/scoped_ptr.hpp>

struct Test
{
  Test(const int x) : m_x(x) {}
  const int m_x;
};

int main()
{
  boost::scoped_ptr<Test> p;
  p->m_x; //Good: uninitialized pointer detected by Boost
}

 

A boost::scoped_ptr can be null, but will check itself for it:

 

#include <boost/scoped_ptr.hpp>

struct Test
{
  Test(const int x) : m_x(x) {}
  const int m_x;
};

Test * CreateNullPointer() { return 0; }

int main()
{
  boost::scoped_ptr<Test> p;
  p.reset(0); //Valid: boost::scoped_ptr can be empty
  p.reset(CreateNullPointer()); //Valid: boost::scoped_ptr can be empty
  p->m_x; //Good: uninitialized pointer detected by Boost
}

 

 

 

 

 

References

 

  1. Scott Meyers. Effective C++ (3rd edition). ISBN:0-321-33487-6. 2005. Item 13: 'Use objects to manage resources'
  2. Scott Meyers. Effective C++ (3rd edition). ISBN:0-321-33487-6. 2005. Item 17: 'Store newed objects in smart pointers in standalone statements'

 

 

 

 

 

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