#define versus const

[Mike Smith]

I have never really understood the difference between

1.) #define NUMBER 1.653

vs.

2.) const double NUMBER = 1.653

I know that the #define is taken care of by the pre-processor and the
compiler is used in the second case but why would one be chosen over the
other.

One book I read suggested that your should prefer the compiler to the
preprocessor, but why does it really matter?

Here's another reason in addition to those already given:

#define MACRO 1.653

const double CONST = 1.653;

double Square(double const *p)
{
return (*p) * (*p);
}

int main()
{
double a = Square(&MACRO); // won't compile

double b = Square(&CONST); // compiles OK

return 0;
}

 

[Tim Slattery]

Here's another reason in addition to those already given:

#define MACRO 1.653

const double CONST = 1.653;

double Square(double const *p)
{
return (*p) * (*p);
}

int main()
{
double a = Square(&MACRO); // won't compile

Certainly not! After the preprocessor finishes with this line it look
like this:

double a = Square(&1.653);

which is meaningless.

double b = Square(&CONST); // compiles OK

CONST is a variable, not a macro, so the preprocessor does nothing to
this line.

 

[Karl Heinz Buchegger]

Certainly not! After the preprocessor finishes with this line it look
like this:

double a = Square(&1.653);

which is meaningless.

Didn't the comment in this line say: won't compile ?

CONST is a variable, not a macro, so the preprocessor does nothing to
this line.

And that's why Mike marked this line as : compiles OK

 

[Dave Moore]

JKop posted:

Luther Baker posted:

JKop wrote:

I'm in Ireland, (and we call them brackets).


Hi JKop,

Curious, what do you call the squared *thingies* in Ireland?

[ ]

-Luther

( ) Brackets

[ ] Square brackets / Block brackets

{ } Chain brackets


Sin a nglaonn muid orthu in Éirinn!


-JKop

As for:

< >


They're not used very much. We'd probably called them Arrow brackets or V
brackets.

How about angle brackets? <g>

Dave Moore

 

[Mike Smith]

Didn't the comment in this line say: won't compile ?




And that's why Mike marked this line as : compiles OK

I suppose I should simply have said that a const object is an object,
and can be treated like one, whereas a literal substitution cannot. <sigh>