C++ pointer to boolean value

Question

I'm having problems trying to implement a class which contains a pointer to a boolean...

class BoolHolder {
    public:
    BoolHolder(bool* _state);

    bool* state;
}

BoolHolder::BoolHolder(bool* _state) {
    state = _state;
}

bool testbool = false;

BoolHolder testbool_holder( &testbool );

If I do this, testbool_holder.state always reports that it is true, no matter whether testbool itself is true or false

What am I doing wrong? I just want the class to be able to maintain an up to date value for testbool but I don't know how to effect this. Thanks

Solution 1

testbool_holder.state returns true if state is not a null pointer

*(testbool_holder.state) returns the value of the bool pointed to by state

Try this for a more C++ solution

class BoolHolder
{
public:
    BoolHolder(bool* state) : state(state) {}
    bool GetState() const { return *state; } // read only
    bool& GetState() { return *state; } // read/write

private:
    bool* state;
}

bool testbool = false;
BoolHolder testbool_holder(&testbool);
if (testbool_holder.GetState()) { .. }

Remove the second getter if you only want to allow read access (and maybe change the pointer to const bool *) If you want both, then you need both getters. (This is because read/write can't be used to read on a const object).

Solution 2

It's right. What you have is not the value of the boolean but a pointer to the boolean. You must dereference the pointer to obtain the value of the bool itself. Since you have a pointer, it will contain an address which is an integer. Since in C and C++ all non zero integers are true, you will get true.