为什么删除操作符会在调试模式下导致调试断言失败？

Question

Recently I noticed that my Engine is absolutely unoptimized so i decide to do a little cleanup. After implementing some of the culling algorithms I open Windows task manager to see how much my application uses memory. In result of my short research about "new" and "delete" operators I tried to use them for more efficiently memory usage. For example:

void DrawSkybox()
{
p_Device->SetRenderState(D3DRS_ZENABLE, D3DZB_FALSE );
D3DXVECTOR3* Scal = new D3DXVECTOR3(1.5f, 1.5f, 1.5f);
D3DXVECTOR3* Rot = new D3DXVECTOR3(0, 0, 0);
obj_Skybox->Transform(&vec3_camera_viewPos, Scal, Rot);
DrawObject(p_Device, obj_Skybox, NULL, NULL, NULL, false);
p_Device->SetRenderState(D3DRS_ZENABLE, D3DZB_TRUE );
delete Scal;
delete Rot;
}

In the first time I compiled and executed debug version of Engine I received an error: "Debug Assertion Failed". Then I compiled and executed my Engine as a Release - everything is just fine. So what is the problem?

Answer 1

You better should refactor your code in this way, instead of bothering about new and delete :

void DrawSkybox() {
     p_Device->SetRenderState(D3DRS_ZENABLE, D3DZB_FALSE );
     D3DXVECTOR3 Scal(1.5f, 1.5f, 1.5f); // <<<< Just use stack 
     D3DXVECTOR3 Rot (0, 0, 0);          // <<<< allocated variables ...
     obj_Skybox->Transform(&vec3_camera_viewPos, &Scal, &Rot); // <<< ... and pass 
                                                               // their addresses
     DrawObject(p_Device, obj_Skybox, NULL, NULL, NULL, false);
     p_Device->SetRenderState(D3DRS_ZENABLE, D3DZB_TRUE );
}

I can't tell anymore details about that actual assertion failure you get, but it's occuring in debug mode only, and release mode compiled code won't notice what's going on.
The errors seem to stem from something different in your code elsewhere, but shouldn't from just introducing the delete statements.