Question

I’m not exactly sure how to pose this question so I’ll start with some example code:

//header file
class A
{
public:
    A();
private:
    int x;
    std::string arr[x];
}

//cpp file

class A
{
public:
    A()
    {
     /*code to get the value of x from a cmd call*/
    }
}

Is this code valid? More specifically, can I have my string array in my header file be of size x, even though x is not specifically given a value until an A object has been created?

If this doesn’t work, is my only other option to use a dynamically allocated array?

Answer 1

The code is not valid. You should use a vector instead.

class A
{
public:
    A();
private:
    int x;
    std::vector<std::string> arr;
};

A::A () : x(command_gets_x()), arr(x) {}

Since arr is being initialized by the value of x, the constructor only works when x precedes arr in A (as it is in your definition). However, if the only purpose of x is to track the size of the array, it is not necessary, since a vector has the size() method.

class A
{
public:
    A() : arr(command_gets_x()) {}
    int x () const { return arr.size(); }
    //...
private:
    std::vector<std::string> arr;
};