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Class / array question

General and Gameplay Programming Programming

Started by DividedByZero October 13, 2015 09:54 PM

9 comments, last by DividedByZero 8 years, 6 months ago

DividedByZero

1,261

Author

October 13, 2015 09:54 PM

Hi Guys,

Not sure if this can be done the way I would like, but I'll put the question out there.

I have an array that contains three floats in each location, which I am using as vertex data.

I have a public variable verticies[] inside a class. Is there a way I can assign variable length data to this variable without the compiler throwing an error?

This is the class (pretty basic)


class Object
{
public:
	Object(){}
	~Object(){}

	VertexPos verticies[];
private:
};

And I'd like to fill the verticies[] like this;


mObject->verticies[] = 
{
	DirectX::XMFLOAT3((float)-0.5, (float)-0.5, (float)0), DirectX::XMFLOAT3((float)-0.5, (float)0.5, (float)0), DirectX::XMFLOAT3((float)0.5, (float)-0.5, (float)0),
	DirectX::XMFLOAT3((float)-0.5, (float)0.5, (float)0), DirectX::XMFLOAT3((float)0.5, (float)0.5, (float)0), DirectX::XMFLOAT3((float)0.5, (float)-0.5, (float)0),
};

Can this be done? Or is this going to be a problem as there is no static size defined in the class?

Thanks in advance

DividedByZero

1,261

Author

October 13, 2015 10:18 PM

I have done this to make the class ready for the amount of verts


	void MakeSpace(int verts)
	{
		verticies = new VertexPos[verts];
	}

	VertexPos* verticies;

How do I set the values? I doesn't seem to be as simple as


mObject->verticies[] = 
{
	DirectX::XMFLOAT3((float)-0.5, (float)-0.5, (float)0), DirectX::XMFLOAT3((float)-0.5, (float)0.5, (float)0), DirectX::XMFLOAT3((float)0.5, (float)-0.5, (float)0),
	DirectX::XMFLOAT3((float)-0.5, (float)0.5, (float)0), DirectX::XMFLOAT3((float)0.5, (float)0.5, (float)0), DirectX::XMFLOAT3((float)0.5, (float)-0.5, (float)0),
};

Thanks again

Madhed

4,095

October 13, 2015 10:20 PM

you can use a std::vector.

If your compiler supports c++11 you can even use the array initializer syntax like in your example.


#include <vector>

class Object
{
public:
	Object(){}
	~Object(){}

	std::vector<VertexPos> vertices;
private:
};

mObject->vertices = { ... }

DividedByZero

1,261

Author

October 13, 2015 10:37 PM

Thanks for the tip. Although I just tried that and the compiler complains of 'C2679 binary '=': no operator found which takes a right-hand operand of type 'initializer list' (or there is no acceptable conversion)'.

I am using VS.net 2015.

Madhed

4,095

October 13, 2015 10:50 PM

Weird, I just tried with VS.net 2015 community edition and it works. Can you post the code of the VertexPos class and the way you initialize the list?

DividedByZero

1,261

Author

October 13, 2015 10:59 PM

Yep, now worries.

This is the class as at now


#pragma once
#include <DirectXMath.h>
#include <vector>

// Structures
struct VertexPos
{
	DirectX::XMFLOAT3 pos;
};

class Object
{
public:
	Object() {}
	~Object() {}

	float x;
	float y;
	float z;
	int nVerts;
	std::vector<VertexPos> vertices;
private:
};

And the initialisation code


Object* mObject = new Object();
mObject->vertices =
{
	DirectX::XMFLOAT3((float)-0.5, (float)-0.5, (float)0), DirectX::XMFLOAT3((float)-0.5, (float)0.5, (float)0), DirectX::XMFLOAT3((float)0.5, (float)-0.5, (float)0),
	DirectX::XMFLOAT3((float)-0.5, (float)0.5, (float)0), DirectX::XMFLOAT3((float)0.5, (float)0.5, (float)0), DirectX::XMFLOAT3((float)0.5, (float)-0.5, (float)0),
};

Thanks heaps for you help

It seems happy enough if I do this


	mObject->vertices[0] = { DirectX::XMFLOAT3((float)-0.5, (float)-0.5, (float)0) };
	mObject->vertices[1] = { DirectX::XMFLOAT3((float)-0.5, (float)0.5, (float)0) };
	mObject->vertices[2] = { DirectX::XMFLOAT3((float)0.5, (float)-0.5, (float)0) };
	mObject->vertices[3] = { DirectX::XMFLOAT3((float)-0.5, (float)0.5, (float)0) };
	mObject->vertices[4] = { DirectX::XMFLOAT3((float)0.5, (float)0.5, (float)0) };
	mObject->vertices[5] = { DirectX::XMFLOAT3((float)0.5, (float)-0.5, (float)0) };

This is far from ideal, as you can imagine

But the 'one line' style initialisation just keeps failing for some reason

Madhed

4,095

October 13, 2015 11:06 PM

Ah!

You are trying to initialize a vector of VertexPos with a list of XMFLOAT3's which is not going to work.

So either you need to make it std::vector<XMFLOAT3> or put another pair of parentheses around the initializer elements like so:


mObject->vertices =
{
	{XMFLOAT3(0,0,0)}, {XMFLOAT3(0,0,0)}, {XMFLOAT3(0,0,0)}
};

DividedByZero

1,261

Author

October 13, 2015 11:12 PM

Nice! That looks like we are back on track!

Thank you so much for your help

Up-voted all of your suggestions, as it is the least I can do in return

DividedByZero

1,261

Author

October 13, 2015 11:23 PM

Just another quick question.

To read the data back, you'd now have to iterate through it like a normal vector, right? (As it doesn't seem to behave like a normal array now).

Class / array question

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