That and the publisher sems to be McGraw here.....hmmm, maybe I''m dumb.

Thnx, I think I''ll really buy that one, especially since you say ALSO and not NO JUST BUY THIS.

That and it''s cheap =)

Imagine you want to print what piece of code is executed as it is executed. One way to do it is to create a string mirroring the code and printing it out :

    {   foo = bar + baz;   if (debug) std::cerr << "foo = bar + baz" << std::endl;}      

However, you have to take care to keep the string and the code in synch. Well, that is what the # macro is for : it converts source code into a string that the source code can use.

          #define STRING( X ) #X{  foo = bar + baz;  if (debug) std::cerr << STRING(foo = bar + baz) << std::endl;}        

Which would not buy you much if you couldn't do things with X within the macro itself :

          #define DBG( X ) { X; if( debug ) std::cerr << #X << std::endl; } /* Executes and prints X */{   DBG( foo = bar + baz );}    

This is what is used in the assert( X ) macro. It tests the value of the expression X, and if it is false, it prints it out and abort().

Edited by - Fruny on November 17, 2001 12:10:13 AM

For multiline macros use a forward slash \ not a backslash - and wrap the multiple statements in a do while loop

Check out the C Language faq for details: What''s the best way to write a multi-statement macro?

late... need... more... caffeine...

wait, but int he macro whats the first X there for?

{X; ...}

whats that X for???

quote: Original post by Sinner_Zero
whats that X for???

To do X.

Remember that X does not necessarily have to be a single variable; it can be a statement (which the preprocessor simply substitutes in place.) For example, in Fruny''s example

foo = bar + baz 

is X. The macro therefore ensures that X is executed, and then only if debug is specified is the rest executed.

IC, X isnt really done since the macro screws it all then.

so the macro hasto actually do X, cool. this stuff is neat.

THNX a ton once again guys, the more I know. heh.