HP 3000 Manuals HP 3000 Manuals
Defining Data Types
The designers of the computer define certain primitive system data types
in order to receive input, store or manipulate data, and return
information in a predictable way.
How a process will use data input depends on the context. If a process
requires a certain data type, it will attempt to interpret input as that
type. For example, if you pass 32 binary bits to an intrinsic parameter
that requires a file address, it may attempt to access the cell at that
location in memory. If you pass the same 32 bits to a parameter that
requires a character array, it may print a four-letter word. If you pass
the same 32 bits to a parameter that requires a 64-bit floating-point
real value, you may cause an error or program abort.
Primitive Data Types
The HP-PA instruction set is designed to operate on certain fundamental
data types. The following data types are recognized by MPE XL and its
subsystems:
* Characters.
* The following numeric types:
* Integers.
* Real numbers (in floating-point notation).
* Decimal.
NOTE Although decimal is not really a system primitive type, it is
included in this manual because it is so widely used on MPE XL.
Floating-point decimals are used by BASIC; packed and unpacked
decimals are used by COBOL and RPG.
Intrinsic Data Types
The compilers of high-level languages running on MPE XL have mechanisms
to access the system-defined procedures called intrinsics. MPE XL
intrinsic parameters recognize the following data types:
Address (@).
Array (A).
Boolean (B).
Character (C).
Integers: Signed (I) and Unsigned (U).
Real (R).
Record (Rec).
Character, integer, and real numbers are system primitive types. Address
and Boolean types are numbers with special uses. Array and record are
structures that group data.
Language Data Types
Some high-level programming languages running on MPE XL define their own
data types based on the primitive types. The language compiler makes any
necessary conversions between the primitive data types and the
language-dependent data types. This conversion is transparent to the
programmer. These types are described in the appropriate language
manuals in the Language Manual Series.
Languages may simply rename the primitive type, like the integer, a
system type common to all languages. Languages may use the system types
as building blocks to create a more complex data structure. For example,
the array is not a primitive type, but is defined by programming
languages as a connected group of data, all of the same type.