Macro substitution and runtime question.

[Chad]

This is taken from page 90 in "The C Programming Language" by Kernighan
and Richtie.

They have the debugging print macro:

#define dprint(expr) printf(#expr " = %g \n", expr)

Which is invoked as in:

dprint(x/y);

The question is, does dprint(x/y) get expanded every time the program
is run (ie I compile it once, but run the program like 200 times), or
only once when the program gets compiled?

[Mike Wahler]

"Chad" <cd*****@gmail.com> wrote in message
news:11*********************@g49g2000cwa.googlegro ups.com...

This is taken from page 90 in "The C Programming Language" by Kernighan
and Richtie.

They have the debugging print macro:

#define dprint(expr) printf(#expr " = %g \n", expr)

Which is invoked as in:

dprint(x/y);

The question is, does dprint(x/y) get expanded every time the program
is run (ie I compile it once, but run the program like 200 times), or
only once when the program gets compiled?

All preprocessing tokens are translated at compile time.

-Mike

[Chad]

Mike Wahler wrote:

"Chad" <cd*****@gmail.com> wrote in message
news:11*********************@g49g2000cwa.googlegro ups.com...

This is taken from page 90 in "The C Programming Language" by Kernighan
and Richtie.

They have the debugging print macro:

#define dprint(expr) printf(#expr " = %g \n", expr)

Which is invoked as in:

dprint(x/y);

The question is, does dprint(x/y) get expanded every time the program
is run (ie I compile it once, but run the program like 200 times), or
only once when the program gets compiled?

All preprocessing tokens are translated at compile time.

-Mike

So in other words, the expression dprint(x/y) doesn't get expanded
every time I run the program?

[Singamsetty]

Chad wrote:

Mike Wahler wrote:

"Chad" <cd*****@gmail.com> wrote in message
news:11*********************@g49g2000cwa.googlegro ups.com...

This is taken from page 90 in "The C Programming Language" by Kernighan
and Richtie.

They have the debugging print macro:

#define dprint(expr) printf(#expr " = %g \n", expr)

Which is invoked as in:

dprint(x/y);

The question is, does dprint(x/y) get expanded every time the program
is run (ie I compile it once, but run the program like 200 times), or
only once when the program gets compiled?

All preprocessing tokens are translated at compile time.

-Mike

So in other words, the expression dprint(x/y) doesn't get expanded
every time I run the program?

.......yes, before actual compilation, the C preprocessor replaces all
"dprint(expr)" statements with printf(#expr " = %g \n", expr). So it
has nothing to do with runtime.

- Singamsetty