Delphi TPath.GetTempPath result is cropped

Question

I am using Delphi 2010 and my program wants to get the system's temp path. I am using TPath.GetTempPath and everything is working fine... at least for me and my coworkers. But on some customer machines this method returns a cropped path which is (of course) not existing. I found out that the problem seems to be the result from underlying call to GetLongPathName().

The complete code looks like this:

[...]
var
 TmpDir : String;
 Len : Integer;
begin

 [... Call to GetTempPath succeeds and we have a valid temp directory in short "~" notation in var TmpDir ...]

 Len := GetLongPathName(PChar(TmpDir), nil, 0);      // Len = 37
    SetLength(TmpDir, Len - 1);                         // We want to set the len of TmpDir to 37 - 1.
    GetLongPathName(PChar(TmpDir), PChar(TmpDir), Len); // Only 32 (instead of 36) characters are copied - so we have a cropped path - But why?!

end;
[...]

This only happens on some systems and I don't know why. I found a nasty workaround for this, but I would like to know what's going on here.

Can somebody put some light on this?

Answer 1

There is a note about this Windows API function on the Homeland Security pages:

"The return buffer for GetLongPathName() and similar functions might return a truncated path and lead to hard-to-find errors."

https://buildsecurityin.us-cert.gov/bsi-rules/home/g1/753-BSI.html

If you have the source code, you could check if the problem described in this article exists in the Delphi 2010 implementation.

Answer 2

What happens if you try:

var
  longpath : string;

SetLength(longpath,MAX_PATH);
SetLength(longpath, GetLongPathName(PChar(TmpDir),PChar(LongPath),MAX_PATH));

This worked for me, your version truncated the path.