std :: vector.resize有时不分配内存？

Question

It seems like std::vector.resize isn't actually allocating memory sometimes. If I run this piece of code:

std::vector<InstanceData> instanceData;
instanceData.resize(meshCount);

float randX = 0.0f;
float randY = 0.0f;
float randZ = 0.0f;

float maxX = 1000.0f;
float maxY = 1000.0f;
float maxZ = 1000.0f;

for(int i = 0; i < meshCount; i++)
{
    randX = (rand() % 100) * 0.01f;
    randY = (rand() % 100) * 0.01f;
    randZ = (rand() % 100) * 0.01f;

    instanceData[i].worldMatrix = DirectX::XMMatrixTranspose(DirectX::XMMatrixTranslation(randX * maxX, randY * maxY, randZ * maxZ));
    instanceData[i].color = DirectX::XMFLOAT4(randX, randY, randZ, 1.0f);
}

The program sometimes crashes when I build for release but seemingly not when I build for debug. I use Visual Studio 2013 to compile.

If I change the resize(meshCount) to reserve(meshCount) (or just remove it) and resort to using a temporary InstanceData which I then just fill with data and push into the vector it seemingly doesn't crash.

If I attach the debugger to the release version it gives me this error message:

Unhandled exception at 0x00BB5BCB in path.exe: 0xC0000005: Access violation reading location 0x00000000.

Any idea what's going on? Why can't I use resize ?

EDIT: Here's InstanceData

struct InstanceData 
{
    DirectX::XMMATRIX worldMatrix;
    DirectX::XMFLOAT4 color;
};

Answer 1

解决方案是使用XMFLOAT4X4代替XMMATRIX