Evaluate preprocessor macro on run time in Inno Setup Pascal Script

Question

I\'m using an Inno Setup #define directive to define all of the information about a software package in my installer and then other directives to extract portions of that st

Answer 1

This cannot work.

The PartNumber is a preprocessor function/macro. It's evaluated on compile time. It does not exist on run time.

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You can, of course, implement an equivalent Pascal Script function:

function PartNumberPascal(Package: string): string;
begin
  Result := Copy(Package, 1, 5);
end;

procedure Foo(Package: String);
var
  PartNumber: String;
begin
  PartNumber := PartNumberPascal(Package);
end;

---

What probably confuses you, is this call:

Foo(ExpandConstant('{#Package1}')); 

It may give you an impression that the ExpandConstant function expands the Package1 preprocessor define.

It does not!

The {#...} syntax (contrary to the {...}) is not a constant. It's an inline preprocessor directive call, where, when no directive is explicitly specified, the emit is implied. So the {#Package1} is the same as {#emit Package1}. And as every preprocessor construct, it's evaluated on compile time.

If you add SaveToFile preprocessor function call to the end of the script:

procedure Bar();
begin
  Foo(ExpandConstant('{#Package1}')); 
end;

#expr SaveToFile(AddBackslash(SourcePath) + "Preprocessed.iss")

And after compilation, check, what the Preprocessed.iss is like. You will see:

procedure Bar();
begin
  Foo(ExpandConstant('05414 - My Package')); 
end;

The Package1 is expanded to its value. But the ExpandConstant is still there, and hence it's totally useless! (there are no constants in the '05414 - My Package')

This would have the same effect:

procedure Bar();
begin
  Foo('{#Package1}'); 
end;

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For a similar question, see:
Evaluate a collection of data from preprocessor on run time in Inno Setup Pascal Script