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NM and CM callable. Reads a logical record or portion of a record from a file to the stack. Syntax | |
I16 I16V UDS I16V
transfercount:=FREAD(filenum,buffer,length);
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Parameters | |
- filenum
16-bit signed integer by value (required) Passes the file number of the file to be read.
If filenum references a directory node, FREAD fails with a
CCL file code.
- buffer
user-defined structure (required) Returns the record that was read. This structure must be large
enough to hold all of the information to be transferred. - length
16-bit signed integer by value (required) Passes the length of the data to be transferred to buffer:
| Value | Meaning |
|---|
| <0 | Length in bytes | | =0 | No transfer occurs | | >0 | Length in half words |
If length is larger than the size of the logical record, and
the multirecord aoption in FOPEN/HPFOPEN was not specified,
transfer is limited to the length of the logical record. If the
multirecord aoption in FOPEN/HPFOPEN is specified,
transfer continues until either length is satisfied or
end-of-data is encountered, and each transfer begins at the start
of the next physical record (block). Any data remaining in the
last physical record read is inaccessible. Data transfer for
byte stream files continues until either length bytes are
read or an end-of-file occurs.
Operation Notes | |
When the logical end-of-data is encountered, CCG (0) is returned to the
process: On magnetic tape, the end-of-data is a physical indicator
such as a tape mark. When the program reads a file that spans more
than one volume of labeled magnetic tape, the program is suspended
until an operator mounts the next tape. CCG (0) is not returned when
end-of-tape is encountered. On disk, the end-of-data occurs when there is an attempt to read
past the last logical record of the file. In this case,
CCG (0) is returned, and no record is read. If the file is embedded in an input source containing commands,
an end-of-data occurs when an EOD command is encountered.
End-of-data is indicated by a hardware end-of-file,
including EOF (on $STDIN), any record beginning with a
colon (:), or on $STDINX, by EOD. On a standard input device for a job (not a session) JOB, EOJ,
or DATA indicate end-of-data.
When reading from an empty message file and another
process has opened that file for write access, the process waits.
If the message file is empty and there are no writers, the
process waits if there is an FCONTROL=45 in effect or if
this is the first FREAD after the reader's FOPEN/HPFOPEN.
Otherwise, CCG (0) is returned. If an FREAD is issued against a
message file and an FCONTROL=46 is in effect, the writer's ID and
the record type code are appended to the beginning of the record. When an old file containing carriage-control characters supplied
through the controlcode parameter of the FWRITE intrinsic is
read, and you specified either the
carriage-control foption parameter of
the FOPEN/HPFOPEN intrinsic, or the CCTL parameter of
the FILE command, the carriage-control byte is read as follows: Figure 4-8 Carriage Control Byte
+-+----------------------------+
|C| |
|C| Data Read |
|B| |
+-+----------------------------+
CCB = Carriage Control Byte
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Condition Codes | |
- CCE (2)
Request granted. The information was read. - CCG (0)
Request denied. The logical end-of-data was encountered
during reading. When reading a labeled magnetic tape file that
spans more than one volume, CCG (0) is not returned when
end-of-tape (EOT) is encountered. CCG (0) is returned at actual
end-of-file, with a transmission log of 0 if there is an attempt to read
past end-of-file. - CCL (1)
Request denied. The information was not read because a terminal
read was terminated by a special character or timeout interval, as
specified in the FCONTROL intrinsic, or a tape error was
recovered and the FSETMODE option was enabled.
Check the condition codes both in normal I/O and in nowait I/O.
Related Information | |
- Intrinsics
None - Commands
None - Manuals
Accessing Files Programmer's Guide (32650-90017)
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