CODEWITHSUNDEEP
c++visual-c++
ph3rin
ph3rin

Reputation: 4850

Visual C++ seems to be zero-initializing POD members of a class which it shouldn't

I have a class like this:

class TestClass
{
public:
    TestClass() {};
    //Note: I wish not to initialize rawMemory (for whatever reason)
    int rawMemory[32];
};

int main()
{
    TestClass obj;
    return 0;
}

And after I created a TestClass object using TestClass obj; I got the behavior I wanted: rawMemory did not get initialized (filled with 0xcc in debug mode and with random undetermined value in release mode).
How ever when I added a pointer member to the class:

class TestClass
{
public:
    TestClass() {};
    int rawMemory[32];
    int* ptr;
};

The rawMemory got initialized to zero! I think according to the standard this should not happen. I even tried with std::aligned_storage which is dedicated for reserving uninitialized automatic memory, and rawMemory still got zero-initialized!

class TestClass
{
public:
    TestClass() {};
    std::aligned_storage<sizeof(int), alignof(int)>::type rawMemory[32];
    int* ptr;
};

Note: I have tried g++, it worked as I expected.
Update: If I change TestClass into a struct, the problem is gone; If I give TestClass a default implicit constructor the problem is gone.

Upvotes: 2

Views: 221

Answers (1)

ph3rin
ph3rin

Reputation: 4850

I have finally found the source of this issue.
When a pointer member is present in the class, Visual C++ inserts a autoclassinit method call before calling the constructor I defined. This method call somewhat messed up with member initialization, and it did zero-initialized my rawMemory member.
This behavior can be removed by disabling /sdl in the Visual C++ compiler options. However, if it is not very performance-critical (or the bottleneck), my suggestion is to leave it as it is.
Thanks to everyone who tried to help!

Upvotes: 4

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