C++ Training

5/25/2018 C++ Training

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SMART POINT


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C++ OBJECT LIFETIME

objects created on the stack are destructed when their scope ends

if FOO has a member variable m_bar, m_bar is destructed when FOO is destructed

1/2C++ Training - Smart Pointers


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STD::SHARED_PTR EXAMPLE 1

void Bar() {

std::shared_ptr spc(new int(5));

Foo(spc); // Both spc and spcParam own the memory while in Foo()

// Now only spc owns the memory

// After Bar completes, spc is destroyed, decrementing the ref count and cleaning up the int itself

}

void Foo(std::shared_ptr spcParam) {

// spcParam is another shared_ptr pointing to the same int. After this function completes, spcParam is destroy

// the ref count on the object is decremented.

}



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STD::SHARED_PTR

standardized in C++11 STL, platform-neutral

ref-counted

access members as you normally would, with ->

be careful of circular references! use std::weak_ptr where needed

dangerous to access object outside of std::shared_ptr/std::weak_ptr



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STD::SHARED_PTR EXAMPLE 2

std::shared_ptr spc1(new int(5));

std::weak_ptr wpc1 = spc1; // spc1 owns the memory.

{

std::shared_ptr spc2 = wpc1.lock(); // Now spc1 and spc2 own the memory.

if(spc2) // Always check to see if the memory still exists

{

// Do something with spc2

}

} // spc2 is destroyed. Memory is owned by spc1.

spc1.reset(); // Memory is deleted.

std::shared_ptr spc3 = wpc1.lock(); // Memory is gone, so we get an empty shared_ptr.



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^ (HAT)

handle to a Windows Runtime object that internally implements IInspectable

create such an object using ref new

ref-counted

access members as you normally would, with ->

be careful of circular references! use WeakReference where needed



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^ EXAMPLE

Foo::Foo()

{

m_Page = ref new Page(); // Foo has a reference to m_Page

WeakReference wrf(this); // m_Page will have a reference to this Foo so create a weak reference to this

m_Page->DoubleTapped += ref new Windows::Ui::Xaml::Input:: DoubleTappedEventHandler(

[wrf](Object^ sender, Windows::Ui::Xaml::Input::DoubleTappedRoutedEventArgs^ args)

{

Foo^ foo = wrf.Resolve(); // Use the weak reference to get the object

if (foo != nullptr) foo->m_eventFired = true;

else throw ref new Platform::DisconnectedException(); // Inform the event that this handler should be rem

});

}



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MORE INFO

std::shared_ptr

MSDN how-to: http://msdn.microsoft.com/en-us/library/hh279669.aspx

C++/CX

Type system reference: http://msdn.microsoft.com/en-us/library/windows/apps/br212455.as

Weak references: http://msdn.microsoft.com/en-us/library/windows/apps/hh699859.aspx

http://msdn.microsoft.com/en-us/library/hh279669.aspxhttp://msdn.microsoft.com/en-us/library/windows/apps/br212455.aspxhttp://msdn.microsoft.com/en-us/library/windows/apps/hh699859.aspxhttp://msdn.microsoft.com/en-us/library/windows/apps/hh699859.aspxhttp://msdn.microsoft.com/en-us/library/windows/apps/hh699859.aspxhttp://msdn.microsoft.com/en-us/library/windows/apps/hh699859.aspxhttp://msdn.microsoft.com/en-us/library/windows/apps/hh699859.aspxhttp://msdn.microsoft.com/en-us/library/windows/apps/br212455.aspxhttp://msdn.microsoft.com/en-us/library/windows/apps/br212455.aspxhttp://msdn.microsoft.com/en-us/library/windows/apps/br212455.aspxhttp://msdn.microsoft.com/en-us/library/windows/apps/br212455.aspxhttp://msdn.microsoft.com/en-us/library/windows/apps/br212455.aspxhttp://msdn.microsoft.com/en-us/library/hh279669.aspxhttp://msdn.microsoft.com/en-us/library/hh279669.aspxhttp://msdn.microsoft.com/en-us/library/hh279669.aspxhttp://msdn.microsoft.com/en-us/library/hh279669.aspxhttp://msdn.microsoft.com/en-us/library/hh279669.aspx


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