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Paged input/output operations buffer all file access by means of an internal paging system, paging being transparent to the application program. The paged input/output system may be accessed explicitly by calling the paged input/output (vdb) routines.
If the application programmer desires to access a dataset by means of the paging system the procedure outlined in the example below may be adopted.
Example 3.1. Access data with paging (Fortran77 example)
Open the databases in buffered (paged) mode:
call opbudb(...)
Get the address of the (existing) dataset which shall be
accessed in paged mode. The word offset of the
dataset is returned in integer*4 variable woff
from subroutine prpdb:
call prpdb(handle,...,woff)
Read and
write data using routines rdwadb and wtwadb (observe the
offset given by woff). The relative offset
ioff takes the values 0, 1, 2,... depending on
the relative address of 4 byte entities (integer*4, real*4) within
the dataset:
call wrvdb(handle,buffer,woff+ioff,nwords,istat)
for writing or
call rdwadb(handle,buffer,woff+ioff,nwords,istat)
for reading.