2 Using OpenVMS Record Management Services

DEC C for OpenVMS systems provides a set of run-time library functions and macros to perform I/O. Some of these functions perform in the same manner as I/O functions found on C implementations running on UNIX systems. Other DEC C functions take full advantage of the functionality of the OpenVMS file-handling system. You can also access the OpenVMS file-handling system from your DEC C program without using the DEC C Run-Time Library (RTL) functions. In any case, the system that ultimately accesses files on OpenVMS systems is OpenVMS Record Management Services (RMS).

This chapter introduces you to the following RMS topics:

• RMS file organization (Section 2.1)

• Record access modes (Section 2.2)

• RMS record formats (Section 2.3)

• RMS functions (Section 2.4)

• Writing DEC C programs using RMS (Section 2.5)

• RMS example program (Section 2.6)

The file-handling capabilities of DEC C fall into two distinct categories:

• The DEC C RTL functions which, with little or no modification, are portable to other C implementations

• The RMS functions, which are not portable to other C implementations, but do provide more methods of file organization and more record access modes

This chapter briefly reviews the basic concepts and facilities of RMS and shows examples of their application in DEC C programming. Because this is an overview, the chapter does not explain all RMS concepts and features. For language-independent information about RMS, see the following manuals in the OpenVMS documentation set:

• Guide to OpenVMS File Applications

  This guide contains a general description of the record management services of the OpenVMS operating system, and the file creation and run-time options available.

• OpenVMS Record Management Services Reference Manual

  This manual describes the user interface to RMS. It includes introductory information on RMS programming and detailed definitions of all RMS control block structures and macro instructions.