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Can file descriptors be reused?
Unlike process IDs, which are recycle only gradually, the kernel always allocates the lowest unused file descriptor when a new descriptor is created. This means that in a multi-threaded program which constantly opens and closes file descriptors, descriptors are reused very quickly.
Why do we have open and close calls for files?
Open() offers a way to lock files while they are in use. If files were automatically opened, read/written and then closed again by the OS there would be nothing to stop other applications changing those files between operations.
Is the file descriptor the same as the file description?
People often confuse these two and think they are the same. File descriptor is an integer in your application that refers to the file description in the kernel. File description is the structure in the kernel that maintains the state of an open file (its current position, blocking/non-blocking, etc.).
Which is the correct integer for a file descriptor?
The descriptor is identified by a unique non-negative integer, such as 0, 12, or 567. At least one file descriptor exists for every open file on the system. File descriptors were first used in Unix, and are used by modern operating systems including Linux, macOS X, and BSD. In Microsoft Windows, file descriptors are known as file handles.
Where are the file descriptors open in a process located?
The process does not have direct access to the file or inode tables. On Linux, the set of file descriptors open in a process can be accessed under the path /proc/PID/fd/, where PID is the process identifier. In Unix-like systems, file descriptors can refer to any Unix file type named in a file system.
Which is the standard file descriptor in Unix?
In the Unix operating system, the standard input is represented by file descriptor 0, the standard output is represented by file descriptor 1 and standard error file is represented by file descriptor 2. In other words, corresponding to the three standard streams, each UNIX process would have three standard file descriptors.