HP 3000 Manuals HP 3000 Manuals
open
Opens a file for reading or writing.
Syntax
#include <fcntl.h>[REV BEG]
int open (char *path, int oflag [,int mode [,char mpe_opts]] );[REV END]
Parameters
[REV BEG]
path A pointer to a path name naming a file.[REV END]
oflag An integer containing open mode bit flags.
mode An unused integer parameter provided for compatibility with
other systems.
mpe_opts A pointer to a string containing file attributes and
options.
Return Values
x Upon successful completion, the integer file descriptor is
returned.
-1 Unsuccessful completion. In addition, errno is set to the
indicated value if one of the following conditions is true:
ENOENT The fname is null, or the named file does not
exist and you did not use oflag to request that
it be created.
EACCES The oflag permission is denied for the named
file.
EMFILE The maximum number of file descriptors allowed
are currently open.
EINVAL The oflag specifies incompatible read/write
access flags.
ESYSERR A call to a system intrinsic failed.
Description
The open function opens the file descriptor described in fname. It uses
the value of oflag to determine how to open the file.
Opening a file in read mode fails if the file does not exist or cannot be
read.
The oflag parameter values are constructed by OR-ing flags from the list
below. Notice that exactly one of the first three flags below must be
used.
O_RDONLY Open for reading only.
O_WRONLY Open for writing only.
O_RDWR Open for reading and writing.
O_APPEND If set, the file pointer is set to the end of the file
prior to each write.
O_CREAT If the file exists, this flag has no effect. If the file
does not exist, the file is created.
O_TRUNC If the file exists, its length is truncated to zero and the
mode and owner are unchanged. The file pointer used to
mark the current position within the file is set to the
beginning of the file.
O_MPEOPTS If this flag is specified, the argument mpe_opts specifies
additional open options that provide greater control in the
MPE file environment.
The mode parameter is ignored. It is provided for compatibility with
other systems.
The mpe_opts argument points to a string of characters described below.
Spaces can be used in the mpe_opts string to improve readability. Notice
that the case of the options is important. An uppercase B is different
from a lowercase b.
b If the b option is specified, the file is created as a
binary file if this call to fopen creates the file. The
default is to create an ASCII file.
Bln The Bl option specifies the blocking factor to use if this
call to fopen() creates the file. The option character is
followed by an integer that indicates the blocking factor.
If the Bl option is not specified, then the default is one
record per block.
[REV BEG]
Bs If the Bs option is specified, the file is opened or
created as a byte stream file. This is the only required
option for opening byte stream files. The maximum file
size for a byte stream file is two gigabytes. If
specified, the Rn option is ignored. The Sn option can be
used to reset the file size. This option is mutually
exclusive with the V option. If the Bs or V options are
not specified, the file is created with an MPE fixed-length
record format.
[REV END]
Bun The Bu option specifies the number of buffers to be
allocated to this file. If the Bu option is not specified,
the default is 2.
C If the C option is specified, then the file accepts
carriage control information. The default is to not have
carriage control.
Dfn The Df option specifies the final disposition of the file
after the file is closed. The affect of each value of n is
defined as follows:
--------------------------------------
| | |
| 0 | Don't change the |
| | disposition. |
| | |
--------------------------------------
| | |
| 1 | Save the file as a |
| | permanent file. |
| | |
--------------------------------------
| | |
| 2 | Save the file as a |
| | temporary file. |
| | |
--------------------------------------
| | |
| 3 | Don't rewind on close. |
| | |
--------------------------------------
| | |
| 4 | Purge the file on close. |
| | |
--------------------------------------
If the Df option is not specified and the file is a new
file, then the default is to save the file as a permanent
file. If the file is old, the default is not to change the
disposition.
Dsn The Ds option specifies the disk space disposition of the
file after the file is closed for fixed, undefined, and
variable format files. The affect of each value of n is
defined as follows:
-----------------------------------------------
| | |
| 0 | Don't return any disk space |
| | allocated beyond the end-of-file |
| | indicator. |
| | |
-----------------------------------------------
| | |
| 1 | Return to the system any disk |
| | space allocated beyond the |
| | end-of-file indicator. The EOF |
| | becomes the file limit. No |
| | records may be added to the file |
| | beyond this new limit. |
| | |
-----------------------------------------------
| | |
| 2 | Return to the system any disk |
| | space allocated beyond the |
| | end-of-file indicator, but do not |
| | set the file limit to EOF, and |
| | allow records to be added to the |
| | file up to the file limit. |
| | |
-----------------------------------------------
If the Ds option is not specified, the default is not to
return any disk space allocated beyond the end-of-file
indicator.
En The E option specifies the maximum number of extents that
can be allocated to the file. The maximum value is 32.
The default value, if the E option is not specified, is 8
extents.
Fn The F option indicates the value used as the file code if
this call to fopen() creates the file. If the F option is
not specified, the file code is zero.
L If specified, the L option indicates that dynamic locking
should be allowed on this file.
Mn The M option controls multiaccess. The option character is
followed by an integer that indicates the level of
multiaccess for this open request. The levels are
specified in the MPE/iX Intrinsics Reference Manual under
the FOPEN intrinsic description.
Q If the Q option is specified, file equations are
disallowed. The default is to allow file equations.
Rn The R option specifies the size of the record if the file
is created by this open request. If the V option is also
used, this option specifies the maximum size of the
variable-sized records. The option letter is followed by a
decimal number that is equal to the number of bytes in the
record size. Notice that the number must be positive. A
byte count is always specified. If the R option is not
provided, then the default record size is 256 bytes.
Sn The S option specifies the maximum size of the file. The
value of n is the maximum size of the file in records for
text and binary streams, and in bytes for byte streams.
Notice that if the S parameter is not specified, the
default is 4095.
Te If the Te option is specified, the file is saved in the
temporary file domain. If the Te option is not specified
and the file is a new file, the default is to save the file
as a permanent file. If the file is old, the default is to
not change the disposition.
Tm If the Tm option is specified, disk read functions trim
editor line numbers, if they exist, and trailing blanks
from each record of an ASCII fixed record length file
before returning file data to the reader. This option is
used on files opened with read only access. Random access
to file data using fseek() and lseek() is not permitted.
The default is to not trim editor line numbers and blanks.
Un If the U option is specified, the file is created with n
user-label records. If this option is not specified, the
default is no user-label records.
[REV BEG]
V If the V option is specified, the file is created with an
MPE variable-length record format. If the V or Bs options
are not specified, then the file is created with an MPE
fixed-length record format. This option is mutually
exclusive with the Bs option.
[REV END]
Xn The X option controls exclusive access ability for the
file. The option character is followed by an integer that
indicates the level of exclusivity for this open request.
The levels are specified in the MPE/iX Intrinsics Reference
Manual under the FOPEN intrinsic.
[REV BEG]
NOTE If linking with the POSIX/iX library, refer to the description of
open() located in the MPE/iX Developer's Kit Reference Manual.
[REV END]
Examples
The following creates or opens a fixed record binary file f1 for writing
with 256 byte records, a file size of 10000 records, and a file code of
1030:
#include <fcntl.h>
int fd;
fd = open("f1",O_WRONLY | O_CREAT | O_MPEOPTS, 0664, "b R256
s10000 F1030");
To open an existing file f1 for reading:
#include <fcntl.h>
int fd;
fd = open("f1",O_RDONLY);
See Also
fopen()