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Introduction

The SAS/C library provides a large set of input/output functions, which are divided into two groups, standard-style I/O functions and UNIX style I/O functions. This chapter describes these functions and how they are used.

The following section describes how to perform input and output using the functions provided in the SAS/C library. This section is important if you use SAS/C I/O facilities, whether you are developing new programs or porting existing programs from other environments.(footnote 1)

The library's I/O implementation is designed to

• support the ISO/ANSI C standard

• support the execution of existing programs developed with other C implementations

• support the development of new portable programs

• support the effective use of native OS/390 and CMS I/O facilities and file types.

As described later in this chapter, the library provides several I/O techniques to meet the needs of different applications. To achieve the best results, you must make an informed choice about the techniques to use. Criteria that should influence this choice are

• the need for portability (For instance, will the program execute on several different systems?)

• the required capabilities (For instance, will the program need to alter the file position randomly during processing?)

• the need for efficiency (For instance, can the program accept some restrictions on file format to achieve good performance?)

• the intended use of the files (For instance, will files produced by the program later be processed by an editor or by a program written in another language?).

To make these choices, you need to understand general C I/O concepts as well as the native I/O types and file structures supported by the 370 operating systems, OS/390 and CMS. These topics are addressed in this chapter. The description is aimed primarily at the knowledgeable C programmer who should be familiar with 370 I/O concepts. In many cases, understanding the 370 I/O concepts is necessary to control and anticipate program behavior. Where possible, this chapter addresses these issues, but familiarizing yourself with 370 I/O concepts using other sources is highly recommended. Chapter 1, "Introduction," of the SAS/C Compiler and Library User's Guide lists the documents from International Business Machines Corporation that may be of particular value.

Some parts of this chapter are intended for knowledgeable 370 programmers who may be interested in the relationship between SAS/C I/O and traditional 370 I/O techniques. These portions are identified as such, and you can skip them if you do not have the necessary background in 370 I/O concepts.

This chapter is divided into two sections: technical background and technical summaries. For the most effective use of SAS/C I/O techniques, you should become familiar with the concepts presented in Technical Background." Skim Technical Summaries for information relevant to your application, and consult specific I/O function descriptions for details on the functions. Much of the material in the last two sections is reference information of limited applicability, but understanding the technical background section is essential for effective use of the library I/O functions.

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