Declaring string constants

fasm has two separate languages on top of each other: the preprocessor and then the assembler. "equ" is a preprocessor's directive, so when you define "OS_VERSION equ WinXP", then it replaces all the occurences of OS_VERSION with WinXP, so what assembler sees is:

Code:

if WinXP = WinXP

and it signalizes an error because the WinXP is nowhere defined.

There is a couple of different solutions how you can make this work. You can define WinXP as a constant for assembler, so that it will recognize it:

Code:

OS_VERSION equ WinXP ; this is for preprocessor

WinXP = 4 ; this is for assembler

if OS_VERSION = WinXP ; after preprocessing this becomes "if WinXP=WinXP"
; ...

The other option is to perform conditional preprocessing instead of conditional assembly, so that everything is done by preprocessor even before assembler has a first peek at the source:

Code:

OS_VERSION equ WinXP

match =WinXP, OS_VERSION {
  ; ...
}

And one more option is to make assembler compare whether given label name is "WinXP" even when the label is not correctly defined, you can do it with "eq" operator:

Code:

OS_VERSION equ WinXP

if WinXP eq WinXP
 ;...

This last option may be the simplest one for you to use.

wyvern wrote:

Another question related, can i define symbols from command line instead changing the values in the source?

No, because of the Same Source, Same Output principle (sometimes called SSSO in short on this forums).