Constants or #define

[subdene]

Which is the best method of storing data that doesn't change? Some people use #define and others constants. It would be good to know when to use const's or #define's.
Thanks.

[Prelude]

In C++ use const.

-Prelude

[ygfperson]

a #define is part of the preprocessor which isn't included in the compiled code. let's say you #define PI 3.1415926535876. before anything else happens, your preprocessor will replace every 'PI' with 3.1415926535876. then your compiler will do its work as usual.

a const is a constant variable. all the rules of c and c++ apply to it.

the biggest advantage to using const variables is type checking. errors are much easier to spot using a const variable than a #define. #defines also tend to mess up in unusual expressions.

in short: use a const. it gives your compiler extra information that can sometimes prevent errors (or at least make them more obvious.)

[subdene]

Thanks for your replies. So when I make a call, to include a #define in my code is a local variable created and then destroyed when the statement has called. Or is the variable destroyed when the program exits? e.g.

#include <iostream.h>

#define MAX_NUM 512

int main(void)
{
  cout << "The maximum num is: " << MAX_NUM;
  getchar();


  return 0;
}

[Unregistered]

#define does not create any variables. The preprocessor changes

#include <iostream.h>

#define MAX_NUM 512

int main(void)
{
  cout << "The maximum num is: " << MAX_NUM;
  getchar();


  return 0;
}

To be:

#include <iostream.h> //This is replaced by the contents of iostream.h



int main(void)
{
  cout << "The maximum num is: " <<512;
  getchar();

  return 0;
}

These codes are equal to the compiler.

[subdene]

With you now. Thanks.