 |
» |
|
|
|
Creates a new file or rewrites an existing file.
Syntax | |
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int creat (const char *pathname, mode_t mode);
|
Parameters | |
- pathname
A pointer to a string containing the pathname of a file to be created or rewritten. The pathname must be terminated by a null character.
- mode
File access permission bits. If the file already exists, mode is ignored. Access permission bits are set by ORing any combination of the following macros:
- S_IRWXU
Set file owner class read, write, and execute (if a file) or search (if a directory) permission bits. - S_IRUSR
Set file owner class read permission bit.
- S_IWUSR
Set file owner class write permission bit.
- S_IXUSR
Set file owner class execute (if a file) or search (if a directory) permission bit.
- S_IRWXG
Set file group class read, write, and execute (if a file) or search (if a directory) permission bits.
- S_IRGRP
Set file group class read permission bit.
- S_IWGRP
Set file group class write permission bit.
- S_IXGRP
Set file group class execute (if a file) or search (if a directory) permission bit.
- S_IRWXO
Set file other class read, write, and execute (if a file) or search (if a directory) permission bits.
- S_IROTH
Set file other class read permission bit.
- S_IWOTH
Set file other class write permission bit.
- S_IXOTH
Set file other class execute (if a file) or search (if a directory) permission bit.
Return Values | |
- >=0
Success. A nonnegative integer is returned representing the lowest numbered file descriptor not open by the calling process.
- -1
An error occurred. The file is not opened, and errno is set to indicate the error condition.
Description | |
The creat() function opens for write-only access a file whose pathname is specified in the string pointed to by pathname.
The creat() function establishes the connection between a file and a file descriptor. It creates an open file description that refers to a file, and a file descriptor that refers to that open file description. The file descriptor is used by other I/O functions to refer to the file.
The creat() function returns a file descriptor for the specified file which is the lowest file descriptor not currently open for the calling process. The open file description is new; therefore, the file descriptor does not share it with any other process in the system.
If the file does not already exist, the file is created and the following occurs:
The file offset is set to the beginning of the file.
The file is opened for O_WRONLY access.
The file's UID is set to the effective UID of the calling process.
The file's GID is set to the GID of the directory in which the file is being created.
The file permission bits of the file are set to mode and modified by the file mode creation mask of the calling process.
The following file time fields are marked for update:
the file's st_atime, st_ctime and st_mtime time fields
the parent directory's st_ctime and st_mtime time fields
If the file already exists, the following occurs:
The file is truncated to zero length, and the file offset is set to the beginning of the file.
The file's UID, GID, and mode remain unchanged.
The st_ctime and st_mtime time fields of the file are marked for update.
The function call
is equivalent to
open (path, O_WRONLY | O_CREAT | O_TRUNC, mode);
|
Implementation Considerations | |
Refer to the EACCES, EEXCL, EFAULT, EIMPL, EINVAL, EMFILE, and ESYSERR error descriptions in the error section of the open() function description.
Pipes (or FIFOs), device special files, and read-only file systems are not supported through POSIX/iX interfaces and cannot be opened by creat(). Device files are inherited from the parent process, which has them opened as STDIN_FILENO, STDOUT_FILENO, and STDERR_FILENO.
The GID of a newly created file is set to the GID of the directory in which the file is created.
MPE/iX file equations are ignored by creat().
The calling process must have the correct access permissions as defined by either an attached ACD or by the MPE/iX file security matrix. The calling process must have either ACD write access and append access or MPE/iX write access and append access.
Signals generated for the calling process during execution of open() are deferred from delivery until completion of this function.
Errors | |
Refer to the error section of the open() function description for errors returned by creat(). Possible errors returned by creat() are the same as those returned by open() when oflag is set to (O_WRONLY | O_CREAT | O_TRUNC).
See Also. | |
open(), close(), dup(), execl(), execv(), <fcntl.h>, lseek(), read(), <signal.h>, fstat(), stat(), <stat.h>, write(), umask(), POSIX.1 (Section 5.3.2)
|
