Handling Files

Working with Transient Data

Transient data files can be either intrapartition or extrapartition data queues. Intrapartition queues are maintained by CICS in a VSAM data set and consist of varying-length records; output to intrapartition queues can also be used to automatically initiate transactions. The default record length for CICS intrapartition transient data queues is 480 bytes (the minimum possible VSAM control interval size of 512, minus 32 bytes of CICS control information).

Extrapartition queues are sequential data sets. They may have fixed- or varying-length records, and they may be blocked and contain ASA control characters. The format of output to extrapartition queues is the following:

[IMAGE]

CC is any ASA carriage control (if the file is defined as recfm=a ).

For high-level programming languages running on CICS, the standard files ( stderr and stdout ) are usually directed to extrapartition transient data queues. Attempts to read from stdin will fail unless the default name is redirected.

Positioning Transient Data Queues

Although transient data queues cannot be positioned, certain input and output operations are still possible for both extrapartition and intrapartition queues. Extrapartition queues used for output can be positioned to EOF (end of file) because output to such files always adds new records to the end of the data set. Thus, these files are always positioned at EOF, which is the only valid position for extrapartition queues. Similarly, input extrapartition queues can be rewound, but only because they are always positioned at the start of the file.

Intrapartition queues can be used for both read and write operations. Records are logically read in the sequence they were written, and output always adds records to the end of the queue. This means that, in effect, intrapartition queues can be rewound because they are always positioned at the start of the file for input, and they can also be positioned to EOF because output always adds new records to the end of the file.

Note: Transient data reads are always destructive; that is, after a record has been read, it cannot be read again. [cautionend]

Specifying Transient Data Filenames

A transient data filename is a four-character symbolic name associated with a specific destination, as defined in the CICS destination control table (DCT). The name can be in uppercase or lowercase, but it is translated to uppercase during processing. The name may refer to an indirect data destination but not to a remote destination. The default destinations associated with the standard files are

File Destination

stdout td:saso

stderr td:sase

stgrpt td:sasr

File	Destination
`stdout`	`td:saso`
`stderr`	`td:sase`
`stgrpt`	`td:sasr`

stgrpt is used for run-time storage analysis and usage reports when the =storage run-time argument is specified. Some examples of specifying transient data filenames follow:

Print "hello world" on stdout:
```
printf("hello world");
```
Open TD queue "logf":
```
f_ptr = fopen("td:logf", "a+");
```

Open and read from TD queue "logf":

f_ptr = fopen("logf", "a+");
fread(string, 1, count, f_ptr);

Redirect stdout to the TD queue "cssl":
```
char *_stdonm = "td:cssl";
```

Amparms for Transient Data

Extrapartition transient data files always exist with predefined file characteristics as they are preallocated and defined to CICS in the DCT. Specifying an amparm will not change the characteristics of an external file; rather, amparms are used to state a program's expectation of the file.

recfm

When using this amparm, consider these points:

An open operation will fail if recfm=f is specified, but the file does not have fixed-length records.
An open operation will fail if recfm=v or recfm=u is specified for an extrapartition file that is opened for output but is actually an F-format file.
No diagnostic is generated if recfm=v or recfm=u is specified for a read-only file.
recfm=u is ignored for intrapartition queues and is treated as recfm=v for extrapartition queues.
Intrapartition queues are always treated as RECFM V files.

reclen

When using this amparm, consider these points:

An open operation will fail for RECFM F files and for RECFM V output files if, for extrapartition queues, reclen=nnn is specified but the actual file's LRECL does not match this specification.
An open operation will fail for RECFM V input files if the specified record length is greater than the actual LRECL of the file.
reclen=x is not supported for transient data queues.
A program's reclen specification is compared to the value of LRECL-4 for a V-format file, not to the LRECL itself. For a file with carriage-control characters, the reclen specification is compared to LRECL-1. Furthermore, extrapartition queues (which are prefixed with four-character terminal and transaction identifiers) are compared to LRECL-8. For example, an extrapartition VBA file with an LRECL of 133 can have at most a reclen specification of 120 (120 from the application + 8 for termid/tranid + 4 for V-format control information + 1 for carriage control).

blksize

When using this amparm, remember that if the actual block size of an extrapartition queue is greater than the size specified by blksize=nnn , a warning will be generated; otherwise, this specification will be ignored.

Default Values

For extrapartition queues, default values for file characteristics amparms ( recfm , reclen , and blksize ) are derived from the values defined in the CICS DCT. For intrapartition queues, the following default values are assigned to the file characteristics amparms:

recfm v

reclen 480

blksize 480

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