Error in array of Labels - C++ Winforms

Question

Friends.

I'm developing a hangman game in C++ Winforms, practically ready, but it's giving an error that I couldn't solve. I want to create an array of Labels. This array has no fixed size. At the beginning of the program I put: static array<Label^>^ labels; To create the labels that will contain the letters of the word drawn, I developed the following snippet: It is giving the error Object reference not set to an instance of an object in line labels[i] = gcnew Label(); Thanks

		void IniciarLabels()
		{
			tam = palavra->Length;

			for (int i = 0; i < tam; i++)
			{
				labels[i] = gcnew Label();
				labels[i]->Font = gcnew System::Drawing::Font("Arial", 26, FontStyle::Bold);
				labels[i]->ForeColor = Color::Black;
				labels[i]->TextAlign = ContentAlignment::MiddleLeft;
				labels[i]->AutoSize = false;
				labels[i]->Size = System::Drawing::Size(40, 40);
				labels[i]->Text = palavra[i] == ' ' ? " " : "_";
				labels[i]->Location = i == 0 ? System::Drawing::Point(X, Y + 5) : System::Drawing::Point((labels[i - 1]->Location.X + 43), Y + 5);
				panel1->Controls->Add(labels[i]);
			}
		}

Answer 1

You appear to have cretaed an array with no elements and no size. You then attempt to assign a new element to a slot in that array via [i] which location doesn't exist.

If your array had a size then you won't get that error, as long as indexer i dosen't exceed that size minus 1.

// Cretae an array of 100 nullptrs.
array<Label^>^ labels = gcnew array<Label^>(100);

int i = 0;

labels[i] = gcnew Label(); // OK now

• Wayne

Answer 2

Note that you can start with an empty array and expand its size as you add elements. There is a fair amount of additional overhead doing this, as new memory allocations have to be created each iteration and the existing elements copied to the new array.

array<Label^>^ labels2;
for (int n = 0; n < 10; ++n)
{
    Array::Resize(labels2, n + 1);
    labels2[n] = gcnew Label();
}

• Wayne

Answer 3

Hi, José Carlos Souza

System.Array is reference type.
Add gcnew array <Label^>(size)before using it.
You could refer to How to: Use Arrays in C++/CLI

array< MyClass^ >^ MyClass0;
MyClass0 = Test0();


array<MyClass^>^ Test0() {
   int i;
   array< MyClass^ >^ local = gcnew array< MyClass^ >(ARRAY_SIZE);

   for (i = 0 ; i < ARRAY_SIZE ; i++) {
      local[i] = gcnew MyClass;
      local[i] -> m_i = i;
   }
   return local;
}

Best regards,

Minxin Yu

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