CODEWITHSUNDEEP
c++class
Cehem
Cehem

Reputation: 83

Using class attribute as array-bound

I would like to do this:

Class Obj{
private:
int a;
int b[a][3];

public:
Obj(int a);
}

So that i can specify the size of my array when creating my object.But I get this compilation error: error: array bound is not an integer constant

I don't want to use vectors, dos anyone know how I can do this? Thanks.

Upvotes: 1

Views: 73

Answers (3)

ForEveR
ForEveR

Reputation: 55897

Array size should be constant. There is only one way, without dynamic allocation - use predefined constant for all arrays of this class.

class Obj{
private:
static constexr int a = 5;
int b[a][3];

public:
Obj();
};

If you want different sizes, then you should allocate memory dynamically, if you don't use vectors.

Upvotes: 1

Saqlain
Saqlain

Reputation: 17928

If you want to depend on extension then ISO C99 allows variable length arrays through extension, have a look at it http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html, with this extension arrays are declared like any other automatic arrays, but with a length that is not a constant expression.

Side effect is your code will compile with compile which got this extension.

Upvotes: 0

Turgal
Turgal

Reputation: 527

You should use a dynamic allocation:

b = new int *[a] ;
//memory allocated for  elements of each column.
for( int i = 0 ; i < a ; i++ )
   b[i] = new int[3];

Upvotes: 0

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