InnoSetup, expand environment variable (taken from registry value using {reg:…} )

Question

I try to set the default install path from the registry:

DefaultDirName={reg:HKCU\\Software\\Microsoft\\VisualStudio\\14.0,VisualStudioLocation|{userdocs}\\Visua         


        

Answer 1

Here is my improved version of ElektroStudios' solution:

It takes care of correct string-termination and does not rely on the 0-termination added by the Win32-function (guess it's not good to use that in Pascal code).

[Code]
#ifdef UNICODE
#define AW "W"
#else
#define AW "A"
#endif

function ExpandEnvironmentStrings(lpSrc: String; lpDst: String; nSize: DWORD): DWORD;
external 'ExpandEnvironmentStrings{#AW}@kernel32.dll stdcall';

function ExpandEnvVars(const Input: String): String;
var
  Buf: String;
  BufSize: DWORD;
begin
  BufSize := ExpandEnvironmentStrings(Input, #0, 0);
  if BufSize > 0 then
  begin
    SetLength(Buf, BufSize);  // The internal representation is probably +1 (0-termination)
    if ExpandEnvironmentStrings(Input, Buf, BufSize) = 0 then
      RaiseException(Format('Expanding env. strings failed. %s', [SysErrorMessage(DLLGetLastError)]));
#if AW == "A"
    Result := Copy(Buf, 1, BufSize - 2);
#else
    Result := Copy(Buf, 1, BufSize - 1);
#endif
  end
  else
    RaiseException(Format('Expanding env. strings failed. %s', [SysErrorMessage(DLLGetLastError)]));
end;