A vector member is reset and unaccessible - c++

Question

I have two projects, one basic client and a dynamic library.
Here's what happens in the client:
int main()
{
Scrutinizer scru;
scru.Scrutinize();
return 0;
}
In the DLL, The Scrutinizer class is as such (__declspec(dllexport) and such omitted for Clarity)
Header
class ProcessesGenerator;
class Scrutinizer
{
public:
Scrutinizer();
~Scrutinizer();
ProcessesGenerator *ProcGenerator
void Scrutinize();
};
The forward declaration of ProcessesGenerator was 'mandatory' for me to avoid some kind of circular reference.
Constructor in .cpp file
Here is how I initialize it:
Scrutinizer::Scrutinizer()
{
ProcGenerator = &ProcessesGenerator();
}
More about this ProcessesGenerator class:
Header
class ProcessesGenerator
{
public:
ProcessesGenerator();
~ProcessesGenerator();
WinFinder winFinder;
std::vector<std::string> fooCollec;
void GenerateProcesses();
};
ProcessesGenerator.cpp
Constructor:
ProcessesGenerator::ProcessesGenerator()
{
//winFinder = WinFinder();//problem will be the same with or without this line
fooCollec = std::vector<std::string>{"one", "two", "three"};
}
A breakpoint in the constructor shows that the vector is initialized with the chosen values.
Problematic function:
void ProcessesGenerator::GenerateProcesses() {
std::string foo = "bar";
fooCollec = std::vector<std::string>{};//read access violation
fooCollec.push_back(foo);//read access violation
winFinder.SomeVector= std::vector<std::string>{};//read access violation
}
Once there, I Can see that the size of vector is reset to 0. Any attempt to re-initialize it, or to push an element results in read access violation .Same with the vecotr member of its WinFinder member. I guess the flaw is obvious, but I really don't get it,
Thanks!

Answer 1

Your problem is with
Scrutinizer::Scrutinizer()
{
ProcGenerator = &ProcessesGenerator();
}
What you are doing is taking the address of a temporary object. That object will be destroyed and the end of that line and you will be left with a pointer that doesn't point to a valid object.
The old way to fix it would be to use
Scrutinizer::Scrutinizer()
{
ProcGenerator = new ProcessesGenerator();
}
But now you have to implement the copy constructor, copy assignment operator, and the destructor. Since you have a modern compiler what you can do instead is make ProcGenerator a std:unique_ptr<ProcessesGenerator> and then Scrutinizer() becomes
Scrutinizer::Scrutinizer() : ProcGenerator(make_unique<ProcessesGenerator>()) {}
I would also like to add that &ProcessesGenerator(); should not even compile. Unfortunately MSVS has a non-standard extension that allows this to compile. You can turn on the /Za compiler option (enforce ANSI compatibility) and then you should get an error like
error C2102: '&' requires l-value

Answer 2

The line ProcGenerator = &ProcessesGenerator(); makes a temporary ProcessesGenerator, takes its address and then puts it in your ProcGenerator pointer. The temporary is then destroyed, leaving garbage.
You probably wanted to be allocating it on the heap ProcGenerator = new ProcessesGenerator; but even in that case I would strongly suggest using unique_ptr instead of a raw pointer.