Why default constructor isn't enough?

[Busin]

class AA
{
public:
const int n;
};

int main()
{
AA a;
....
}

This code gives error: "C2512: 'AA' : no appropriate default constructor
available."

Then adding a constructor fixes the error.

class AA
{
public:
const int n;
AA(int m) : n(m) {}
};

int main()
{
AA a(1);
...
}

Can someone elaborate why with a const member variable, the default
constructor isn't enough? Thanks!

 

[Thomas J. Gritzan]

class AA
{
public:
const int n;
};

Your const variable has to be initialized at construction time, because it
could not be changed later.

Thomas

 

[Ali Cehreli]

class AA
{
public:
const int n;
};

int main()
{
AA a;
...
}

This code gives error: "C2512: 'AA' : no appropriate default constructor
available."

Then adding a constructor fixes the error.
[...]


Can someone elaborate why with a const member variable, the default
constructor isn't enough? Thanks!

What I understand from this is that a const member can only be
initialized in the initialization list, which requires a constructor.

Ali

 

[JKop]

Busin posted:

Can someone elaborate why with a const member variable, the default
constructor isn't enough? Thanks!

Looks like you must initialize a const variable.


-JKop

 

[Devesh Mandowara]

If there is an initialiser list...its enough
-Devesh