Re: Is extended const common practice?

Victor Bazarov <>
Thu, 27 May 2010 11:26:50 -0400
On 5/27/2010 11:00 AM, DeMarcus wrote:

I'm using extended const like the following.

// ExtConst.hpp
#ifndef EXT_CONST
#define EXT_CONST

#include <string>

struct ExtConst
ExtConst( double value, const std::string& description )
: value(value), description(description) {}

const double value;
const std::string description;


// Constants.hpp

#include "ExtConst.hpp"

const ExtConst PI( 3.1415, "Circumference / diameter." );
const ExtConst E( 2.71828, "Euler's constant." );


// Now I use ExtConst.hpp in several files since const in front of
ExtConst ensures internal linkage (?7.1.1/7).

// An example.
#include "Constants.hpp"

int main()
std::cout << "Constant: " << E.value
<< " Description: " << E.description << std::endl;

Are constants made up of whole classes or structures common practice?

Actually, constants are generally not common practice, at least from
what I have been able to determine in the places where I have worked.

 > Do

you use that in your projects, and if not, is there a reason?

Constants like PI, E, are self-documenting. Constants whose source
isn't obvious usually have comments next to their definitions.

Other things, like parts of the system that don't usually change during
the run-time are most often defined in special configuration files that
are read at the run time. And in those files they are documented. The
reason is not to have to change the source code (and rebuild, etc.) when
it's determined that some constant has to be adjusted.

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