IBM Version 4 Manipulating a User Space without Pointers, Position Values, Lengths, Space APIs

Manipulating a User Space without Pointers

Manipulating a User Space without Pointers

When programming in a language that does not support pointers, you can Change User Space (QUSCHGUS) and Retrieve User Space (QUSRTVUS) API to manipulate data. However, you must first understand how to use po lengths with these APIs.

Position Values

Some APIs return offset values into a user space. To use other APIs Retrieve User Space (QUSRTVUS) API, you must use position values to bytes.

Position values

and

offset

values

are

different

ways to

express

the

offset

value

is

the

relative

distance

of

a byte

from

the

first

byte

which

has

an

offset valuepositionof value0.

A

is

the offset

value

plus 1.

For examples of HLL programs that use positions, see “List Object API Example” on page 5-4.

Lengths

List APIs return the length of the information in the different sect space, as well as the length of the list entries in the user spac your application using the lengths returned instead of specifying the

returned by the API or the				size of a data structure			in	the dat
amount	of	information	returned	for	any format	may increase	in	future
the information will be placed				at the end of the existing				informatio
your application to function properly, it should retrieve the								length o
returned and add that length				to	a pointer or to a starting			position
Using	Offset	Values with	the Change	and	Retrieve User	Space
APIs

When you use the Change User Space (QUSCHGUS) or Retrieve User Sp (QUSRTVUS) API, your application program should first retrieve the of the information you want. You must then add one to the offset value starting position for the information.

Changing a User Space—Example

Before and after illustrations show how the QUSCHGUS API changes a space. The following is a user space before you change it with one examples.

Chapter 2. Getting Started with2-17APIs