Re: Declare a member variable of a class in the constructor

From:

"Jonathan Mcdougall" <jonathanmcdougall@gmail.com>

Newsgroups:

comp.lang.c++

Date:

13 May 2006 13:46:47 -0700

Message-ID:

<1147553207.710434.123510@j73g2000cwa.googlegroups.com>

ankurd...@gmail.com wrote:

Is it possible to declare a class member variable in the constructor?
For example,

class SomeClass
{
    public:
        SomeClass()
            { int SomeArray[10]; }
}

In this example, is it possible to make SomeArray[] a member variable
without putting the declaration like this:

class SomeClass
{
    public:
        SomeClass();
    private:
        int SomeArray[10];
}

No, that's impossible.

The reason I am asking this is that I would like to create an array
whose size is determined by the parameters passed into the constructor.

Either

1) dynamically allocate it:

class SomeClass
{
public:
  SomeClass(const std::size_t size)
  {
    SomeArray = new int[size];
  }

  ~SomeClass()
  {
    delete[] SomeArray;
  }

private:
  int* SomeArray;
};

and do read about the "rule of three" (see especially chapter 16 of the
FAQ).

or

2) use a standard container

# include <vector>

class SomeClass
{
public:
  SomeClass(const std::size_t size)
    : v(size)
  {
  }

private:
  std::vector<int> v;
};

Note that in particular a) standard containers manage their own memory
and b) they can grow as needed so the "size" argument is not necessary
(except for performance).

comp.lang.c++ FAQ: http://www.parashift.com/c++-faq-lite/

Jonathan