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std::auto_ptr or boost::shared_ptr for pImpl idiom?

Asked 2008-11-22T10:03:34.860
16

When using the pImpl idiom is it preferable to use a boost:shared_ptr instead of a std::auto_ptr? I'm sure I once read that the boost version is more exception friendly?

class Foo
{
public:
    Foo();
private:
    struct impl;
    std::auto_ptr<impl> impl_;
};

class Foo
{
public:
    Foo();
private:
    struct impl;
    boost::shared_ptr<impl> impl_;
};

[EDIT] Is it always safe to use std::auto_ptr<> or are there situations when an alternative boost smart pointer is required?

c++ boost stl shared-ptr auto-ptr
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2 Answers

4

The boost alternative to std::auto_ptr is boost::scoped_ptr. The main difference from auto_ptr is that boost::scoped_ptr is noncopyable.

See this page for more details.

answered 2008-11-22T10:25:36.797
1

If you want a copyable class, use scoped_ptr, which forbids copying, thus making your class hard to use wrong by default (compared to using shared_ptr, the compiler won't emit copy facilities on its own; and in case of shared_ptr, if you don't know what you do [which is often enough the case even for wizards], there would be strange behaviour when suddenly a copy of something also modifies that something), and then out-define a copy-constructor and copy-assignment:

class CopyableFoo {
public:
    ...
    CopyableFoo (const CopyableFoo&);
    CopyableFoo& operator= (const CopyableFoo&);
private:
    scoped_ptr<Impl> impl_;
};

...
CopyableFoo (const CopyableFoo& rhs)
    : impl_(new Impl (*rhs.impl_))
{}
answered 2011-08-10T15:02:33.153

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