Pointer Member Variable Initialization in C++ Classes

Question

This is going to sound so basic as to make one think I made zero effort to find the answer myself, but I swear I did search for about 20 minutes and found no answer.

Answer 1

Value will be undefined.

You may have one "ultimate" ctor which will initialize all fields and add "short-cut" ctors with only part of parameters, which will pass these params to ultimate ctor along with default values for the rest of params.

Answer 2

You're thinking correctly. If you don't initialise it, it could be anything.

So the answer to your question is yet, either initialise it with something, or give it a NULL (or nullptr, in the most recent C++ standard).

class A
{
};


class B
{
private:
    A* a_;

public:
    B() : a_(NULL) { };
    B(a* a) : a_(a) { };
};

Our default ctor here makes it NULL (replace with nullptr if needed), the second constructor will initialise it with the value passed (which isn't guaranteed to be good either!).

Answer 3

The value will be uninitialised so yes you do need to explicitly initialise it to nullptr.

Using smart pointers (std::unique_ptr, std::shared_ptr, boost::shared_ptr, etc.) would mean that you don't need to do this explicitly.

Answer 4

the value of any uninitialized pointer is always garbage, it's some random memory address.

in your constructors, you can use initializer lists to initialize your pointer

simply

MyClass::MyClass() : myPointer(nullptr)
{
}

trying to reference an uninitialized pointer triggers undefined behavior. so ALWAYS initialize your pointer.