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The Windows API imposes a maximum filename length such that a filename, including the file path to get to the file, can't exceed 255-260 characters.
In editions of Windows before Windows 10 version 1607, the maximum length for a path is MAX_PATH, which is defined as 260 characters. In later versions of Windows, changing a registry key or using the Group Policy tool is required to remove the limit.
The maximum combined length of the file name and path name is 1024 characters. The Unicode representation of a character can occupy several bytes, so the maximum number of characters that a file name might contain can vary. On Linux: The maximum length for a file name is 255 bytes.
In Windows 10, you can enable long file name support, which allows file names up to 32,767 characters (although you lose a few characters for mandatory characters that are part of the name). To enable this, perform the following: Start the registry editor (regedit.exe)
Individual components of a filename (i.e. each subdirectory along the path, and the final filename) are limited to 255 characters, and the total path length is limited to approximately 32,000 characters.
However, on Windows, you can't exceed MAX_PATH value (259 characters for files, 248 for folders). See http://msdn.microsoft.com/en-us/library/aa365247.aspx for full details.
It's 257 characters. To be precise: NTFS itself does impose a maximum filename-length of several thousand characters (around 30'000 something). However, Windows imposes a 260 maximum length for the Path+Filename. The drive+folder takes up at least 3 characters, so you end up with 257.
This is what the "Unhandled exception" says on framework 4.5 when trying to save a file with a long filename:
The specified path, file name, or both are too long. The fully qualified file name must be less than 260 characters, and the directory name must be less than 248 characters.
199 on Windows XP NTFS, I just checked.
This is not theory but from just trying on my laptop. There may be mitigating effects, but it physically won't let me make it bigger.
Is there some other setting limiting this, I wonder? Try it for yourself.
The length in NTFS is 255. The NameLength field in the NTFS $Filename attribute is a byte with no offset; this yields a range of 0-255.
The file name iself can be in different "namespaces". So far there are: POSIX, WIN32, DOS and (WIN32DOS - when a filename can be natively a DOS name). (Since the string has a length, it could contain \0 but that would yield to problems and is not in the namespaces above.)
Thus the name of a file or directory can be up to 255 characters. When specifying the full path under Windows, you need to prefix the path with \\?\ (or use \\?\UNC\server\share for UNC paths) to mark this path as an extended-length one (~32k characters). If your path is longer, you will have to set your working directory along the way (ugh - side effects due to the process-wide setting).
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