How to - Iterate through a Platform::Collections Vector? Visual C++ WinRT

Question

I've read up on the new Collections classes, but the documentation has no examples on how to iterate through the Map or Vector collection types.

It would help me out a lot if somebody could help fill in this for loop:

for(Platform::Collections::VectorIterator^ it = ...

I am not seeing any "begin" or "end" functions in the Platform::Collections::Vector class..

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Land Of Simeria - http://www.stormsonggames.com/los

Answer 1

The Platform::Collection::Vector and std::vector method names are different, but are similar.

For example, instead of using std::vector::begin(), use Platform::Collection::Vector::First()

See Vector methods here http://msdn.microsoft.com/EN-US/library/hh441570(v=VS.110,d=hv.2).aspx

Alternatively, you can use ranged base for loops. Same syntax for std::vector and Platform::Collection::Vector

Platform::Collections::Vector<int> ^vect;
vect = ref new Vector<int>();
vect->Append(1);
vect->Append(7);
for (int i:vect)
    sum+=i;

Note that you can store ^ pointers in a std::vector:

std::vector<myClass^> vect;
vect.push_back(ref new myClass());

Answer 2

I saw that there is a First() function, but no Last, or End.  How can you setup a for loop?

Is this the only way?

unsigned int vectorSize = myVector->Size;
for(unsigned int i = 0; i < vectorSize; ++i)
{
	//... myVector->GetAt(i);
}

I find it really odd that you cannot walk through a container using iterators.

for(Platform::Collections::VectorIterator^ it = myVector->First(); it != ???; ++it)
{
...
}

What should be written in place of "???"

Also, I'm really curious what your code does:

for (int i:vect)
    sum+=i;

I've never seen this syntax before. What is happening here?

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Land Of Simeria - http://www.stormsonggames.com/los

Answer 3

2 ways to loop in a Platform::Collections::Vector

Vector<int> ^vect;
for (int item:vect)
{
    sum+=item;
}

// or :
for (IIterator<int> ^it = vect->First(); it->HasCurrent; it->MoveNext())
{
    int item = it->Current;
    sum+=item;
}

I don't like the 2nd one, so I use the 1st one.

But I guess the generated code is the same in the 2 cases.

You can't use "++it" because ^it is not a C++ pointer.

Answer 4

Wow, thanks Pierre!  That is awesome!!

One related question, do you know how we can create a Vector and initialize it with contents from another Vector?

I tried this, but doesn't work:

Platform::Collections::Vector<int>^ vector2 = ref new Platform::Collections::Vector<int>(vector1);

Also, you must have a ton of experience with Visual C++ and WinRT.. because the documentation has basically no examples of iteration. :P

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Land Of Simeria - http://www.stormsonggames.com/los

Answer 5

Also, I'm really curious what your code does:

for (int i:vect)
    sum+=i;

I've never seen this syntax before. What is happening here?

It is the new C++11 "range based for" statement. You can use it to loop through enumerable types like std::vector or Platform::Collections::Vector. See http://msdn.microsoft.com/en-us/library/jj203382.aspx or search on the web for "range based for".

Answer 6

You are welcome !

As far as I know, you cannot create a Vector from another Vector. But you can create a Vector from a Platform::Array. And you can create a Platform::Array from a Vector.

So, using a temporary Array, you can create a Vector and initialize it with content from another Vector:

	Vector<int> ^vect1;
	vect1 = ref new Vector<int>();
	vect1->Append(1);
	vect1->Append(7);
	Platform::Array<int, 1> ^tmpArray = ref new Array<int, 1>(10);
	vect1->GetMany(0, tmpArray);
	Vector<int> ^vect2 = ref new Vector<int>(tmpArray);
	// or vect2->ReplaceAll(tmpArray);

Of course, you can also copy Vector items one by one. I don't know which is faster.

Alternatively you can use plain old std::vector (vector<reftype^>) instead of Vector...