| open(), creat() | |
|---|---|
| open and possibly create a file or device | |
| #include 'sys/types.h' #include 'sys/types.h' #include 'fcntl.h' int open( const char *pathname, int flags); int open( const char *pathname, int flags, mode_t mode); int creat( const char *pathname, mode_t mode); |
Given a pathname for a file, open() returns a file descriptor, a small, nonnegative integer for use in subsequent system calls (read(2), write(2), lseek(2), fcntl(2), etc.). The file descriptor returned by a successful call will be the lowest-numbered file descriptor not currently open for the process.
By default, the new file descriptor is set to remain open across an execve(2) (i.e., the FD_CLOEXEC file descriptor flag described in fcntl(2) is initially disabled; the O_CLOEXEC flag, described below, can be used to change this default). The file offset is set to the beginning of the file (see lseek(2)).
A call to open() creates a new open file description, an entry in the system-wide table of open files. This entry records the file offset and the file status flags (modifiable via the fcntl(2) F_SETFL operation). A file descriptor is a reference to one of these entries; this reference is unaffected if pathname is subsequently removed or modified to refer to a different file. The new open file description is initially not shared with any other process, but sharing may arise via fork(2).
The argument flags must include one of the following access modes: O_RDONLY, O_WRONLY, or O_RDWR. These request opening the file read- only, write-only, or read/write, respectively.
open() and creat() return the new file descriptor, or -1 if an error occurred (in which case, errno is set appropriately).