How can I use language files with custom messages with preprocessor constants?

Question

I want to have all CustomMessages in language files (extension isl). Also, some of the messages contain preprocessor constants, e.g.

ALREADY_INSTALLED={#MyAppName} is already installed on this computer.

The message should be displayed like this:

"My-really-nice-App is already installed on this computer"

But what I get is:

"{#MyAppName} is already installed on this computer."

The following works like a charm when I have the code, the message defined in a [CustomMessages]-topic and #define MyAppName in the same iss file:

MsgBox(ExpandConstant('{cm:ALREADY_INSTALLED}'), ...);

Any clues?

Answer 1

Only .iss file is preprocessed, not .isl files.

But you can use FmtMessage function:

FmtMessage(CustomMessage('ALREADY_INSTALLED'), ['{#MyAppName}'])

With

ALREADY_INSTALLED=%1 is already installed on this computer.

Note that in Pascal Script code, you better use CustomMessage('FOO'), instead of ExpandConstant('{cm:FOO}').

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Similar question: Pass parameters to custom messages defined in .isl files.

If you need to preprocess the standard messages, see Can I use .isl files for the messages with preprocessor directives in Inno Setup?