External Interfaces

Your program can interface with its external environment (other routines and files supported by the operating system) by using physical files, external routines, and intrinsics.

A physical file is a program-independent entity that the operating system maintains. It can be a permanent file on a disk or other medium, or it can be an interactive file created at a terminal. Your program can manipulate a physical file by associating it with a logical file (a file that the program declares). Chapter 3, "Input/Output," explains physical and logical files, which HP Pascal programs use for input/output.

An external routine is a routine that is not in the compilation unit that calls it. Its source language can be HP Pascal, HP C, HP COBOL II/XL, HP FORTRAN 66/V, HP FORTRAN 77, or SPL. Your program can access an external routine by declaring it with the EXTERNAL directive. Chapter 9 explains external routines.

An intrinsic is an external routine that can be called by a program written in any language that the operating system supports. An intrinsic can be written in any supported language, but its formal parameters must be of types that have counterparts in all the other supported languages. Your program can access an intrinsic by declaring it with the INTRINSIC directive. You need not declare the intrinsic's entire parameter list, and your program can use an intrinsic function as either a function or a procedure. Refer to Chapter 10 “Intrinsics ” for more information on intrinsics.