C++ index out of range NOT occurring when it should

Question

I'm trying to write a OBJMesh loader at the moment in DirectX and I came across a problem with a section of my code:

unsigned int vertexCount = vertexData.size();
VERTEX* vertices = new VERTEX[vertexCount];
std::copy(vertexData.begin(), vertexData.end(), vertices);

The vertexData in the std::copy is a vector<VERTEX> and I'm trying to copy the data in vertexData to my newly created vertices array.

when I load in my objmesh file, I have checked there are 2841 vertices which is correct and I've stored it to vertexCount (I've checked it by doing a std::cout << vertexCount).

However, the real problem is that when I check the data and size of the array by entering std::cout << vertices[3000].x it prints out something without triggering the index out of bound error.

Knowing I've created the vertices array with a size of 2841, the compiler should stop and display a error should it not? What exactly is the problem and why is it behaving like this??

Please help

EDIT: using Visual Studio 2010 Windows 7 64bit

Which compiler? Which operating system? Many compilers have some ways to enable "checked" iterators and indexing functions. — bennofs, Jul 02 '13 at 18:57
Which part of the standard supports your claim that your program should crash and display an error? — chris, Jul 02 '13 at 18:57
Your vertices are just an ordinary array. No bound checking. — ondrejdee, Jul 02 '13 at 18:58

score 1 · Accepted Answer · answered Jul 02 '13 at 18:57

1

The behaviour of vertices[3000].x is undefined. The compiler/runtime are not obliged to provide any diagnostic.

answered Jul 02 '13 at 18:57

NPE

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score 0 · Answer 2 · answered Jul 02 '13 at 18:58

0

Accessing an element beyond the end of an array in C++ is undefined behavior. That basically means that anything can happen and that you should not be expecting any particular result or error.

answered Jul 02 '13 at 18:58

David Rodríguez - dribeas

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score 0 · Answer 3 · answered Jul 02 '13 at 18:59

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What you do leads to undefined behavior. anything can happen, you can absolutely not expect out of bounds exception. Which you could realistically get only if used std::vector and accessed elements using .at() instead of [].

answered Jul 02 '13 at 18:59

Balog Pal

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C++ index out of range NOT occurring when it should

3 Answers3