Using Environment variables to load a file from My Pictures

It’s been a while since I used Environment Variables in Delphi and I had to look it up.

I have a loose rule that anything I have to look up, I want to share on my blog so that I can find it again easily later.

So here you have it: Enviromental Variable expansion ala Delphi.

It’s really not that complex, and it’s possible that this routine could be optimized some. But I think it works well enough as is and demonstrates the use of ExpandEnvironmentStrings quite nicely. If you need to get a list of the variables, you’ll need to do further research on GetEnvironmentStrings and FreeEnvironmentStrings to return the list to you for manipulation. A search for FreeEnvironmentStrings Delphi gives you pleanty of code examples.

Here is my example for ExpandEnvironmentStrings:

[delphi]
var
ImageFileName, FullFileName: string;
BufSize: Integer;
NewPath: String;
begin
// Retrieve the contents of the edit field into a local variable for ease of use.
ImageFileName := Edit1.Text;

// If it exists in the working path, use that as our retrieval point.
// Otherwise, look in the Application directory, then the My Pictures folder,
// then look in the Windows directory
if (FileExists(ImageFileName))
then FullFileName := ImageFileName // Working directory needs no path.
else if (FileExists(ExtractFilePath(Application.ExeName) + ImageFileName))
then FullFileName := ExtractFilePath(Application.ExeName) + ImageFileName // Grab the path from the application executible info
else begin

// Use environmental variables to locate two other possible places
// Allow 254 character paths to be returned.
SetLength(NewPath, 254);

// Call ExpandEnvironmentStrings with string containing environmental variables
BufSize := ExpandEnvironmentStrings(‘%userprofile%\My Documents\My Pictures\’, PChar(NewPath), 254);

// The returned BuffSize must be used to truncate off any extra garbage & injections.
SetLength(NewPath, BufSize – 1);

// Look for it and if it is found, assign the full name otherwise keep looking.
if (FileExists(NewPath + ImageFileName))
then FullFileName := NewPath + ImageFileName
else begin
// Repeat the above process for the Windows Directory.
SetLength(NewPath, 254);
BufSize := ExpandEnvironmentStrings(‘%windir%\’, PChar(NewPath), 254);
SetLength(NewPath, BufSize – 1);
if (FileExists(NewPath + ImageFileName))
then FullFileName := NewPath + ImageFileName
else FullFileName :=’NOT FOUND’;
end;
end;
[/delphi]

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