Where do I define symbols tested with {$IFDEF}?

Question

When I use Delphi directives in code, like:

{$IFDEF something}
.
.
.
{$ENDIF}

Where do I assign the word 'something' in the project? I tried in some places in project options but it didn't work. Guess I didn't find the correct one.

Answer 1

It's in the Conditional Defines slot under Project | Options, which looks like this on D2010:

Answer 2

Other answers have pointed you at the places to define symbols and the scope implications of the different approaches.

However, what no-one has yet mentioned is that if you change the DEFINE symbols you MUST do a FULL BUILD of your project for them to have any effect on your code.

When you "Compile" the Delphi compiler will only compile units which have themselves changed since the previous compile. If you change DEFINE symbols this doesn't change any project units, so if the units are not re-compiled then the change in DEFINE symbols will not have ANY effect in those units.

To FORCE changes in DEFINE symbols to be applied in ALL units, you MUST "build", not compile.

This may explain why your attempt to set defines did not appear to work previously