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Windows File Paths#

File Paths Formats#

Traditional DOS Path#

  • standard DOS path can consist of three components:

  • volume/drive letter + volume separator (i.e. :)

  • directory name: directory separator (i.e. \,/) delimits nested subdirectories
  • optional filename: directory separator separates file path vs filename

  • qualification

  • absolute: all three components are present

  • relative to current drive root: no volume/drive letter is specified and directory name begins with directory separator
  • relative to current directory: all other cases
    |Dos Path Example|Description|
    |----------------|-----------|
    |C:\Documents\Newsletters\Summer2018.pdf|An absolute file path from the root of drive C:.|
    |\Program Files\Custom Utilities\StringFinder.exe|A relative path from the root of the current drive.|
    |2018\January.xlsx|A relative path to a file in a subdirectory of the current directory.|
    |..\Publications\TravelBrochure.pdf|A relative path to a file in a directory starting from the current directory.|
    |C:\Projects\apilibrary\apilibrary.sln|An absolute path to a file from the root of drive C:.|
    |C:Projects\apilibrary\apilibrary.sln|A relative path from the current directory of the C: drive.|

UNC Path#

  • has following format

  • \\ + server/host name; name can be NetBIOS machine name/IPv4/IPv6/FQDN address

  • \ + share name; the volume is defined by combining server + share name
  • directory name: directory separator delimits nested subdirectories
  • optional filename: directory separator separates file path vs filename
  • must always be fully qualified; any relative directory segments (i.e. .,..) must be part of fully qualified path
UNC Path Example Description
\\system07\C$\ The root directory of the C: drive on system07.
\\Server2\Share\Test\Foo.txt The Foo.txt file in the Test directory of the \\Server2\Share volume.

Device Path#

  • windows has a unified object model that points to all resources, including files

  • object paths exposed to the Win32 layer through special folders of symbolic links that legacy DOS and UNC paths are mapped to

  • \\?\: Win32 file namespaces special folder e.g. \\.\C:\Test\Foo.txt
    • tells the Windows APIs to disable all string parsing and to send subsquent string straight to the file system
    • this also turns off automatic expansion of the path string
    • allows you to do
    • exceed MAX_PATH limits usually enforced by the Windows APIs (assuming file system supports large paths)
    • use ..,. in path names which can be useful if attempting to perform operations on file with illegal qualified path

  • \\.\: Win32 device namespaces special folder e.g. \\?\C:\Test\Foo.txt

    • direct access to physical device, disk, or volume disks and volumes; bypasses filesystem
    • ex: CreateFile with \\.\PhysicalDrive1,\\.\CdRomX

    • [!danger] only use \\.\ prefix to access devices only and not files; most APIs won't support it

  • or by a volume's GUID
    \\.\Volume{b75e2c83-0000-0000-0000-602f00000000}\Test\Foo.txt
    \\?\Volume{b75e2c83-0000-0000-0000-602f00000000}\Test\Foo.txt

  • DOS device path consists of:

  • device path specifier: i.e. \\.\ or \\?\

  • symbolic link to the "real" device object (e.g. C: for drive name, Volume{b75e2c83-0000-0000-0000-602f00000000} for volume GUID)

    • first path segment after the device path specifier identifies the volume or drive (e.g. \\?\C:\ or \\.\BootPartition\.)
    • UNC: specific link for UNC paths
      \\.\UNC\Server\Share\Test\Foo.txt
      \\?\UNC\Server\Share\Test\Foo.txt
    • for UNC device paths, the server+share segments form the volume

  • e.g. \\?\server1\e:\utilities\\filecomparer\, the server/share portion is server1\utilities

  • means it's never possible to navigate past the volume with relative directory segments
  • DOS device path is fully qualified by definition

Example Paths#

These all point to the same file

  • c:\temp\test-file.txt
  • \\127.0.0.1\c$\temp\test-file.txt
  • \\LOCALHOST\c$\temp\test-file.txt
  • \\.\c:\temp\test-file.txt
  • \\?\c:\temp\test-file.txt
  • \\.\UNC\LOCALHOST\c$\temp\test-file.txt
  • \\127.0.0.1\c$\temp\test-file.txt

Path Normalization#

  • Identifies path type
Path Type Identification
device path begin with \\? or \\.
UNC path begin with \\
fully qualified DOS path begin with drive letter+volume separator+component separator .e. C:\
legacy device e.g. CON, LPT1
relative to current drive root begin with single component separator \
relative to specific drive current directory begin with drive letter+volume separator without component separator e.g. C:
relative to current directory everything else e.g. temp\testfile.txt

  • Applies the current directory to partially qualified (relative) paths

  • Canonicalizes component and directory separators

  • Evaluates relative directory components (. for the current directory and .. for the parent directory)

  • Trims certain characters

References#