creat

Creates a new file.

Format

#include  <fcntl.h>

int creat  (const char *file_spec, mode_t mode);
           (ISO POSIX-1)

int creat  (const char *file_spec, mode_t
           mode, . . . ); (DEC C
           Extension)

Arguments

file_spec

A null-terminated string containing any valid file specification.

mode

An unsigned value that specifies the file-protection mode. The compiler performs a bitwise AND operation on the mode and the complement of the current protection mode.

You can construct modes by using the bitwise OR operator (|) to create mode combinations. The modes are as follows:

0400 OWNER:READ

0200 OWNER:WRITE

0100 OWNER:EXECUTE

0040 GROUP:READ

0020 GROUP:WRITE

0010 GROUP:EXECUTE

0004 WORLD:READ

0002 WORLD:WRITE

0001 WORLD:EXECUTE

The system is given the same privileges as the owner. A WRITE privilege implies a DELETE privilege.

Note

To create files with OpenVMS RMS default protections using the UNIX system-call functions umask, mkdir, creat, and open, call mkdir, creat, and open with a file-protection mode argument of 0777 in a program that never specifically calls umask. These default protections include correctly establishing protections based on ACLs, previous versions of files, and so on. In programs that do vfork/exec calls, the new process image inherits whether umask has ever been called or not from the calling process image. The umask setting and whether the umask function has ever been called are both inherited attributes.

>.H.>.

An optional argument list of character strings of the following form:

"keyword = value", . . . ,"keyword = value"

Or in the case of "acc" or "err", this form:

"keyword"

Here, keyword is an RMS field in the file access block (FAB) or record access block (RAB); value is valid for assignment to that field. Some fields permit you to specify more than one value. In these cases, the values are separated by commas.

The RMS callback keywords "acc" and "err" are the only keywords that do not take values. Instead, they are followed by a pointer to the callback routine to be used, followed by a pointer to a user- specified value to be used as the first argument of the callback routine. For example, to set up an access callback routine called acc_callback whose first argument is a pointer to the integer variable first_arg in a call to open, you can use the following statement:

open("file.dat", O_RDONLY, 0 ,"acc", acc_callback, &first_arg)

The second and third arguments to the callback routine must be pointers to a FAB and RAB, respectively, and the routine must have a return type of int. If the callback retruns a value less than 0, the open, creat, or fopen fails. The error callback can correct the error condition and return a status greater than or equal to 0 to continue the creat call. Assuming the previous open statement, the function prototype for acc_callback would be similar to the following statement:

#include <rms.h>

int acc_callback(int *first_arg, struct FAB *fab, struct RAB *rab);

FAB and RAB are defined in the <rms.h> header file, and the actual pointers passed to the routine are pointers to the RAB and FAB being used to open the file file.dat.

If an access callback routine is established, then it will be called in the open-type routine immediately before the call to the RMS function sys$create or sys$open. If an error callback routine is established and an error status is returned from the sys$create or sys$open function, then the callback routine will be invoked immediately after the status is checked and the error value is discovered.

Note: Any manipulation of the RAB or FAB in a callback function could lead to serious problems in later calls to the DEC C RTL I/O functions.

Table 5 describes the RMS keywords and values.

Table 5 RMS Valid Keywords and Values

Keyword	Value	Description
"acc"	callback	Access callback routine.
"alq = n"	decimal	Allocation quantity.
"bls = n"	decimal	Block size.
"ctx = bin"	string	No translation of '\n' to the terminal. Use this for writing binary data to files.
"ctx=cvt"	string	Negates a previous setting of "ctx=nocvt". This is the default.
"ctx = nocvt"	string	No conversion of Fortran carriage-control bytes.
"ctx = rec"	string	Force record mode access.
"ctx = stm"	string	Force stream mode access.
"ctx=xplct"	string	Causes records to be written only when explicitly specified by a call to fflush, close, or fclose.
"deq = n"	decimal	Default extension quantity.
"dna = filespec"	string	Default file-name string.
"err"	callback	Error callback routine.
"fop = val, val , . . . "		File-processing options:
	ctg cbt dfw dlt tef cif sup scf spl tmd tmp nef rck wck mxv rwo pos rwc sqo	Contiguous. Contiguous-best-try. Deferred write; only applicable to files opened for shared access. Delete file on close. Truncate at end-of-file. Create if nonexistent. Supersede. Submit as command file on close. Spool to system printer on close. Temporary delete. Temporary (no file directory). Not end-of-file. Read check compare operation. Write check compare operation. Maximize version number. Rewind file on open. Current position. Rewind file on close. File can only be processed in a sequential manner.
"fsz = n"	decimal	Fixed header size.
"gbc = n"	decimal	The requested number of global buffers for a file.
"mbc = n"	decimal	Multiblock count.
"mbf = n"	decimal	Multibuffer count.
"mrs = n"	decimal	Maximum record size.
"pmt=usr-prmpt"	string	Prompts for terminal input. Any RMS input from a terminal device will be preceded by "usr-prmpt" when this option and "rop=pmt" are specified.
"rat = val, val . . . "		Record attributes:
	cr blk ftn none prn	Carriage-return control. Disallow records to span block boundaries. FORTRAN print control. Explicitly forces no carriage control. Print file format.
"rfm = val"		Record format:
	fix stm stmlf stmcr var vfc udf	Fixed-length record format. RMS stream record format. Stream format with line-feed terminator. Stream format with carriage-return terminator. Variable-length record format. Variable-length record with fixed control. Undefined.
"rop = val, val . . . "		Record-processing operations:
	asy	Asynchronous I/O.
	cco	Cancel Ctrl/O (used with Terminal I/O).
	cvt	Capitalizes characters on a read from the terminal.
	eof	Positions the record stream to the end-of-file for the connect operation only.
	nlk	Do not lock record.
	pmt	Enables use of the prompt specified by "pmt=usr-prmpt" on input from the terminal.
	pta	Eliminates any information in the type-ahead buffer on a read from the terminal.
	rea	Locks record for a read operation for this process, while allowing other accessors to read the record.
	rlk	Locks record for write.
	rne	Suppresses echoing of input data on the screen as it is entered on the keyboard.
	rnf	Indicates that Ctrl/U, Ctrl/R, and DELETE are not to be considered control commands on terminal input, but are to be passed to the application program.
	rrl	Reads regardless of lock.
	syncsts	Returns success status of RMS$_SYNCH if the requested service completes its task immediately.
	tmo	Timeout I/O.
	tpt	Allows put/write services using sequential record access mode to occur at any point in the file, truncating the file at that point.
	ulk	Prohibits RMS from automatically unlocking records.
	wat	Wait until record is available, if currently locked by another stream.
	rah	Read ahead.
	wbh	Write behind.
"rtv=n"	decimal	The number of retrieval pointers that RMS has to maintain in memory (0 to 127,255).
"shr = val"		File sharing options:
	del get mse nil put upd upi	Allows users to delete. Allows users to read. Allows mainstream access. Prohibits file sharing. Allows users to write. Allows users to update. Allows one or more writers.
"tmo = n"	decimal	I/O timeout value.

In addition to these options, any option that takes a key value (such as "fop" or "rat") can be negated by prefixing the value with "no". For example, specify "fop=notmp" to clear the "tmp" bit in the "fop" field.

Notes

While these options provide much flexibility and functionality, many of them can also cause severe problems if not used correctly.
You cannot share the default DEC C for OpenVMS stream file I/O. If you wish to share files, you must specify "ctx=rec" to force record access mode. You must also specify the appropriate "shr" options depending on the type of access you want.

For more information on these options, see the OpenVMS Record Management Services Reference Manual manual.

Description

The DEC C RTL opens the new file for reading and writing, and returns the corresponding file descriptor.

If the file exists:

A version number one greater than any existing version is assigned to the newly created file.
By default, the new file inherits certain attributes from the existing version of the file unless those attributes are specified in the creat call. The following attributes are inherited:
- Record format (fab$b_rfm)
- Maximum record size (fab$w_mrs)
- Carriage control (fab$b_rat)
- File protection

If the file did not previously exist:

It is given the file protection that results from performing a bitwise AND on the mode argument and the complement of the current protection mask.
It defaults to stream format with line-feed record separator and implied carriage-return attributes.

See also open, close, read, write, and lseek in this section.

Return Values

n A file descriptor.

-1 Indicates errors, including protection violations, undefined directories, and conflicting file attributes.

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0400	OWNER:READ
0200	OWNER:WRITE
0100	OWNER:EXECUTE
0040	GROUP:READ
0020	GROUP:WRITE
0010	GROUP:EXECUTE
0004	WORLD:READ
0002	WORLD:WRITE
0001	WORLD:EXECUTE