Paths
The path to a specified file consists of one or more components, separated by a special character (a backslash), with each component usually being a directory name or file name, but with some notable exceptions discussed below. It is often critical to the system's interpretation of a path what the beginning, or prefix, of the path looks like. This prefix determines the namespace the path is using, and additionally what special characters are used in which position within the path, including the last character.
If a component of a path is a file name, it must be the last component.
Each component of a path will also be constrained by the maximum length specified for a particular file system. In general, these rules fall into two categories: short and long. Note that directory names are stored by the file system as a special type of file, but naming rules for files also apply to directory names. To summarize, a path is simply the string representation of the hierarchy between all of the directories that exist for a particular file or directory name.
Fully Qualified vs. Relative Paths
For Windows API functions that manipulate files, file names can often be relative to the current directory, while some APIs require a fully qualified path. A file name is relative to the current directory if it does not begin with one of the following:
- A UNC name of any format, which always start with two backslash characters ("\\"). For more information, see the next section.
- A disk designator with a backslash, for example "C:\" or "d:\".
- A single backslash, for example, "\directory" or "\file.txt". This is also referred to as an absolute path.
If a file name begins with only a disk designator but not the backslash after the colon, it is interpreted as a relative path to the current directory on the drive with the specified letter. Note that the current directory may or may not be the root directory depending on what it was set to during the most recent "change directory" operation on that disk. Examples of this format are as follows:
- "C:tmp.txt" refers to a file named "tmp.txt" in the current directory on drive C.
- "C:tempdir\tmp.txt" refers to a file in a subdirectory to the current directory on drive C.
A path is also said to be relative if it contains "double-dots"; that is, two periods together in one component of the path. This special specifier is used to denote the directory above the current directory, otherwise known as the "parent directory". Examples of this format are as follows:
- "..\tmp.txt" specifies a file named tmp.txt located in the parent of the current directory.
- "..\..\tmp.txt" specifies a file that is two directories above the current directory.
- "..\tempdir\tmp.txt" specifies a file named tmp.txt located in a directory named
tempdir that is a peer directory to the current directory.
Relative paths can combine both example types, for example "C:..\tmp.txt". This is useful because, although the system keeps track of the current drive along with the current directory of that drive, it also keeps track of the current directories in each of the different drive letters (if your system has more than one), regardless of which drive designator is set as the current drive.