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In Unix and related computer operating systems, a file descriptor (FD, less frequently fildes) is an abstract indicator used to access a file or other input/output resource, such as a pipe or network connection. File descriptors form part of the POSIX application programming interface. A file descriptor is a non-negative integer, represented in C programming language as the type . Each Unix process (except perhaps a daemon) should expect to have three standard POSIX file descriptors, corresponding to the three standard streams: ==Overview== In the traditional implementation of Unix, file descriptors index into a per-process ''file descriptor table'' maintained by the kernel, that in turn indexes into a system-wide table of files opened by all processes, called the ''file table''. This table records the ''mode'' with which the file (or other resource) has been opened: for reading, writing, appending, reading and writing, and possibly other modes. It also indexes into a third table called the ''inode table'' that describes the actual underlying files. To perform input or output, the process passes the file descriptor to the kernel through a system call, and the kernel will access the file on behalf of the process. 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. As well as regular files, this includes directories, block and character devices (also called "special files"), Unix domain sockets, and named pipes. File descriptors can also refer to other objects that do not normally exist in the file system, such as anonymous pipes and network sockets. The FILE data structure in the C standard I/O library usually includes a low level file descriptor for the object in question on Unix-like systems. The overall data structure provides additional abstraction and is instead known as a ''file handle.'' 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「File descriptor」の詳細全文を読む スポンサード リンク
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