I want to use some variables that are declared as public in one source and as extrn in another. And I want to use the same header for this.

In C I can do this



But for this to work in fasm I need to know if a macro has being defined or not.
In the manual I found the keyword used can be used to know if a symbol is being used.
But I dont know how to know if a symbol as being declared or not.

Does someone know how to do this?

See fasm faq.

Thank you,

So basically equ is declared in the preprocessor stage, while = is done at the assembler stage.

Thats why this did not work
[code]
MyHeader_Internal = 1

if defined MyHeader_Internal
; Private
else
;public
end if
[/b]

But this do
[code]
MyHeader_Internal equ 1

if defined MyHeader_Internal
; Private
else
; public
end if
[/b]

Two suggestions:
1. Include the FAQ inside the zip distribution.
2. Make the keywords bold in the pdf documentation so they could not be easily skipped. After some searching I did find defined in the manual (near the explanation for used with no examples.

you got it wrong. First one DOES work, but i quess you didn't realize that "if" is handled at assembly time, so preprocessor code will be taken from both parts.

Here both "a" and "c" will be defined, because "equ"s (and all preprocessor stuff) is handled before handling "if". FASM's "if" is
something else than C's #if, C's one is preprocess-time, while in assembly it is handled later.
By the way, second code works in other manner than you thought,
with "MyHeader_Internal equ 1" code is preprocessed to

If it isn't defined then assembled code is

so it checks for constant named "MyHeader_Internal" (for example label), and suposing you haven't any label/constant of such name, condition is false.
Also [url=http://decard.net/?body=tajga&chapter=preproc my preprocessor tutorial[/url] might clear it for you.