therning.org/ magnus

Sometimes RAII is difficult.

The following code compiles without errors or warnings on Windows using Visual Studio 2005:

#include <iostream>
#include <memory>

namespace Test
{

    class Foo
    {
    public:
        bool should_do_stuff() { return false; }
    };

    class Bar
    {
    public:
        Bar(std::auto_ptr<Foo> fp) : _fp(fp) {}

        void do_stuff() {
            if(_fp->should_do_stuff())
                std::cout << "Do stuff" << std::endl;
            else
                std::cout << "Don't do stuff" << std::endl;
        }

    private:
        std::auto_ptr<Foo> _fp;
    };

} // Test


int
main()
{
    std::auto_ptr<Test::Foo> fp;
    fp = new Test::Foo;

    bp->do_stuff();

    return(0);
}

However, it throws an exception just at the end of execution. Hmm, strange. Compiling it using GCC fails—it complains about the lack of an applicable operator= function.

This is what the assignment should look like:

fp = std::auto_ptr<Test::Foo>(new Test::Foo);

With that change GCC accepts it, and Microsoft’s compiler generates exception-free code.