#define leads to the "Access violation reading location" - c++

Question

I think this is child question but i can't find info how to solve it.
//*.h:
class Foo
{
#if defined(RedefChallangesCount)
static const mainDataType ChallangesCount = 500;
#undef RedefChallangesCount
#else
static const mainDataType ChallangesCount = 1;
#endif
...
int _correctAnswers[ChallangesCount];
....
}
In my VS tests class:
#include "stdafx.h"
#include "CppUnitTest.h"
#define RedefChallangesCount
#include "..\Core\ChallengeManager.h"
using namespace Microsoft::VisualStudio::CppUnitTestFramework;
using namespace Brans;
namespace CoreTests
{
TEST_CLASS(SomeTestClass)
{
public:
TEST_METHOD(SomeTestMethod)
{
Foo* cm = new Foo();
cm->Method();
...
delete cm;
}
}
}
It seems for me that i do all like in docs, but when run test with #define RedefChallangesCount line i got strange errors like "Access violation reading location", sometimes bad array
_correctAnswers. At the same time i see that ChallangesCount is 500 as expected. If i comment #define RedefChallangesCount line - all errors gone...
What can be wrong?

Answer 1

Your #undef makes me suspicious that this header is being included elsewhere (e.g by ChallengeManager.cpp, meaning you'll end up with your _correctAnswers having a size of 500 in some places and 1 in others, which would certainly explain your crash.
(edit): Are your tests a separate project in the solution, with the main code in its own project, or is your code all compiled directly in the test project?
To be safe, set your #define in the VS build configuration (for all projects being linked into the tests - you'll need to add a Tests build config for this, and use it instead of Debug/Release for the test build) rather than defining it in code, and remove the #undef

Answer 2

I tend not to have if defined sections within code, especially class code. I would tend to use a variable, and branch based on its value:
in the test class remove the #define RedefChallangesCount and replace with a global variable of bool RedefChallangesCount
Then your code becomes much simpler and can be as follows (simplified version for demonstration purposes):
#include <iostream>
using namespace std;
bool RedefChallangesCount = false;
int main()
{
int ChallangesCount;
cout << RedefChallangesCount << endl;
if (RedefChallangesCount)
ChallangesCount = 500;
else
ChallangesCount = 1;
cout << ChallangesCount << endl;
return 0;
}
as opposed to:
#if defined(RedefChallangesCount)
static const mainDataType ChallangesCount = 500;
#undef RedefChallangesCount
#else
static const mainDataType ChallangesCount = 1;
#endif
However, let me know if using preprocessor is a requirement and then I can try and sort you out a solution using that methodology, though as I said, I don't use preprocessor directives for actual program flow (have to add normally, as guaranteed I have done it once for a valid reason, and cant remember).