Inno Setup - #define directive - how to use previously defined variable?

Question

I am using Inno Setup version 5.4.2.

I want to define the path for the files to copy (the Source: parameter in the [Files] section as two parts, a base path and sub-directory names, that I use for special files (like .dlls). I have tried the following:

#define MyAppSetupDir "D:\MyApp\setup"
#define MyAppSetupQtDLLs {#MyAppSetupDir}"\DLLs"
[Files]
Source: {#MyAppSetupDir}\MyApp.exe; DestDir: {app}; Flags: ignoreversion
Source: {#MyAppSetupDLLs}\mstext35.dll; DestDir: {app}; Flags: ignoreversion

but I get the following compilation error

[ISPP] Expression expected but opening brace ("{") found.

I also tried to enclose the braces in "", like

#define MyAppSetupQtDLLs "{#MyAppSetupDir}\DLLs"

But this time I got

Error: Source file "D:\MyApp\setup\{#MyAppSetupDir}\DLLs\mstext35.dll" does not exist.

So, ISSP is correctly replacing the MyAppSetupDir variable, but then puts again the simple text, as if it did not recognize the directive.

I have searched everywhere, and I already found a discussion about using the {commonappdata}, but I could not find how to do this, neither in the documentation nor in the KB. I would really appreciate some hints, as it looks I am close, but not finding the right solution..

Solution

#define MyAppSetupDir "D:\MyApp\setup"
#define MyAppSetupQtDLLs MyAppSetupDir + "\DLLs"