Windows – Why does %TEMP% resolve to a non-deterministic path of the form %TEMP\

tempwindowswindows-server-2008

I have a Windows Server 2008 32 bit and when I'm typing %temp% it takes me to ..AppData\Local\Temp\1\ or ..AppData\Local\Temp\2 instead of ..AppData\Local\Temp

I've already checked the Environment Variables and they are ok.

I'm asking that because I have an application that's supposed to copy files to %temp%\my application and instead it copies the files to %temp%\1\my application

Does someone have a solution for that?

Best Answer

Explanation, discussion, workarounds, etc, all under the Old New Thing article Why does the name of my TEMP directory keep changing - it ensures multiple terminal services sessions for the same user don't (by default) share a temp directory.

The problem lay in the Administrative Templates\Windows Components\Terminal Services\Temporary folders group policy. If you don't select Do not use temporary folders per session, then these TEMP subdirectories are created. There is also a knowledge base article describing the registry keys behind these group policies.

Personally, I find the first comment in reply to be the most useful:

Why does it matter if the temp location jumps around anyway, it's temporary!

Maximum Path Length Limitation

In the Windows API (with some exceptions discussed in the following paragraphs), the maximum length for a path is MAX_PATH, which is defined as 260 characters. A local path is structured in the following order: drive letter, colon, backslash, name components separated by backslashes, and a terminating null character. For example, the maximum path on drive D is "D:\some 256-character path string<NUL>" where "<NUL>" represents the invisible terminating null character for the current system codepage. (The characters < > are used here for visual clarity and cannot be part of a valid path string.)

Now we see that it is 1+2+256+1 or [drive][:\][path][null] = 260. One could assume that 256 is a reasonable fixed string length from the DOS days. And going back to the DOS APIs we realize that the system tracked the current path per drive, and we have 26 (32 with symbols) maximum drives (and current directories).

The INT 0x21 AH=0x47 says “This function returns the path description without the drive letter and the initial backslash.” So we see that the system stores the CWD as a pair (drive, path) and you ask for the path by specifying the drive (1=A, 2=B, …), if you specify a 0 then it assumes the path for the drive returned by INT 0x21 AH=0x15 AL=0x19. So now we know why it is 260 and not 256, because those 4 bytes are not stored in the path string.

Why a 256 byte path string, because 640K is enough RAM.

Java – Windows temp directory details (Java)

This will give you the path to the windows temp directory in Java.

File.createTempFile("temp-file", "tmp").getParent()

Windows – Why does %TEMP% resolve to a non-deterministic path of the form %TEMP\

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Windows – Why does the 260 character path length limit exist in Windows

Java – Windows temp directory details (Java)

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