"Variable expected" error when using Inno Setup StringChangeEx function

Question

I am using Inno Download Plugin to download a bunch of files for my installation. These files are listed in "files.json".

FileList := TStringList.Create;
FileList.LoadFromFile(ExpandConstant('{tmp}\files.json'));
  
for i := 0 to FileList.Count-1 do
begin
  fileName := ExtractFileName(FileList[i]);
  
  StringChangeEx(FileList[i], '\', '/',True);

  //Add each file to download queque
  idpAddFile("www.myapiaddress.com/files/" + FileList[i], ExpandConstant('{tmp}\install\') + fileName );
  Log(FileList[i]);
end;

What gives me a headache is the line StringChangeEx(FileList[i], '\', '/',True). As soon as I put that in, the idp.iss stops compiling, giving me the error: Variable expected on

procedure idpAddFile(url, filename: String);                     external 'idpAddFile@files:idp.dll cdecl';

Installer compiles normal, if I remove StringChangeEx from my script entirely. It does not help to place it in a different location...

Any idea, what might cause this problem?

Answer 1

The StringChangeEx function needs a string variable in the first argument (it's declared as var). You are giving it a string value only.

Your code would work, were FileList a string array. But it's not, it's a class with an array-like string default property. Using a property value is an equivalent of using a function/method return value. A property is just syntactic sugar for getter and setter methods.

You will have to copy the value to a string variable and back.

S := FileList[i];
StringChangeEx(S, '\', '/',True);
FileList[i] := S;

Though you actually do not need to copy it back in your case.

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Regarding the reason why the error refers to idp.iss file: There seems to be a bug in Inno Setup that makes it report the error as if it had occurred on the very first line of the Pascal Script code (what in your case is the very first real code in the included idp.iss). I've posted a bug report. It was fixed already.