CSREVW — View an object and sequentially access it

Call CSREVW if you reference data in a sequential pattern and you want to:

Map a window to one or more blocks (4096 bytes) of a data object. If you specified scrolling when you called CSRIDAC to identify the object, CSREVW maps the window to the blocks in the scroll area and maps the scroll area to the object.
Specify how many blocks window services is to bring into the window each time CSREVW needs more data from the object.

Mapping a data object enables your program to access the data that is viewed through the window the same way it accesses other data in your storage.

The CSREVW and CSRVIEW services differ on how to specify sequential access:

If you use CSRVIEW and specify sequential, when you reference data that is not in your window, window services reads up to 16 blocks — the one that contains the data your program requests, plus the next 15 consecutive blocks. The number of consecutive blocks varies, depending on the size of the window and the availability of central storage.
If you use CSREVW, you can specify the number of additional consecutive blocks that window services reads into the window at one time. The number ranges from 0 through 255.

Use CSREVW if your program has sequential access and can benefit from having more than 16 blocks come into a window at one time, or fewer than 16 blocks at one time.

Code the CALL following the syntax of the high-level language you are using and specifying all parameters in the order shown below. For parameters that CSREVW uses to obtain input values, assign appropriate values. For parameters that CSREVW ignores, assign any value that is valid for the particular parameter’s data type.

To map a window to a data object and begin viewing the object, specify BEGIN and SEQ and assign values, acceptable to CSREVW, to:
- object_id
- offset
- span
- window_name
- disposition
- pfcount
CSREVW returns values in return_code and in reason_code.
To end the view and unmap the data object, use CSRVIEW END and specify all values, except for pfcount, that you specified when you mapped the window.

CALL statement	Parameters
CALL CSREVW	(operation_type ,object_id ,offset ,span ,window_name ,usage ,disposition ,pfcount ,return_code ,reason_code)

operation_type

Specify BEGIN to request that CSREVW map a data object.

,object_id

Specifies the object identifier. Supply the object identifier that CSRIDAC returned when you obtained access to the object.

Define object_id as character data of length 8.

,offset

Specifies the offset of the view into the object. Specify the offset in blocks of 4096 bytes.

Define offset as integer data of length 4.

,span

Specifies the window size in blocks of 4096 bytes.

Define span as integer data of length 4.

,window_name

Specifies the symbolic name you assigned to the window in your address space.

,usage

Specify SEQ to tell CSREVW that the expected pattern of references to data in the object will be sequential.

Define this field as character data of length 6. Pad the string on the right with 1 blank.

,disposition

Defines how CSREVW is to handle data that is in the window when you begin a view. When you specify CSREVW BEGIN and a disposition of:

REPLACE: The first time you reference a block to which the window is mapped, CSREVW replaces the data in the window with the data from the referenced block.
RETAIN®: When you reference a block to which the window is mapped, the data in the window remains unchanged. When you call CSRSAVE to save the mapped blocks, CSRSAVE saves all of the mapped blocks because CSRSAVE considers them changed.

Define disposition as character data of length 7. If you specify RETAIN, pad the string on the right with 1 blank.

,pfcount

Specifies the number of additional blocks you want window services to bring into the window each time your program references data that is not already in the window. The number you specify is added to the minimum of one block that window services always brings in. That is, if you specify a value of 20, window services brings in a total of 21. The number of additional blocks ranges from zero through 255.

Define pfcount as integer data of length 4.

,return_code

When CSREVW completes, return_code contains the return code. Define return_code as integer data of length 4.

Return codes and reason codes are explained under Return codes and reason codes.

,reason_code

When CSREVW completes, reason_code contains the reason code. Define reason_code as integer data of length 4.

Return codes and reason codes are explained under Return codes and reason codes.