Declare array size in header file without #define's

Question

I have a code a following (simplified version):

#define MESSAGE_SIZE_MAX 1024
#defined MESSAGE_COUNT_MAX 20

class MyClass {
public:
   .. some stuff
private:
   unsigned char m_messageStorage[MESSAGE_COUNT_MAX*MESSAGE_SIZE_MAX];
};

I don't like defines, which are visible to all users of MyCalss.

How can I do it in C++ style?

Thanks Dima

avakar · Accepted Answer · 2009-07-22 15:28:51Z

7

Why don't you simply use a constant?

const int message_size_max = 1024;

Note that unlike C, C++ makes constant variables in global scope have static linkage by default.

The constant variable above is a constant expression and as such can be used to specify array sizes.

char message[message_size_max];

answered Jul 22, 2009 at 15:28

avakar

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2 Comments

dimba Over a year ago

It will be statically linked in all objects using MyClass and thus adding garbage to them.

avakar Over a year ago

If it does, then you have an ancient compiler or you're taking the constant's address somewhere.

nik · Accepted Answer · 2009-07-22 15:12:10Z

6

The trick to get such things into the class definition is,

// public:
enum {MESSAGE_SIZE_MAX=1024, MESSAGE_COUNT_MAX=20};

I never liked #defines to be used like constants.
Its always a good practice to use enum.

answered Jul 22, 2009 at 15:12

nik

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