Introduction

Input/output depends on files: your program reads input from files and writes output to files. The terms that describe the three varieties of input/output — sequential, textfile, and direct — also describe the associated files.

This chapter:

Gives general information about files.
Explains the predefined file-opening procedures and how they determine whether files are sequential or direct, for input or for output.
Defines sequential as it applies to input/output and files, and explains the predefined routines that support sequential I/O.
Explains textfile input/output and files, which are subsets of sequential I/O and files (respectively), and explains the routines peculiar to them.
Defines direct as it applies to input/output and files, and explains the predefined routines that support direct I/O.
Gives the conditions under which files are closed, and tells what happens when a file closes.

Figure 3-1 “Relationships Between I/O Varieties and File Types ” illustrates the relationships between sequential, textfile, and direct input/output and sequential files, textfiles, and direct files.

Figure 3-1 Relationships Between I/O Varieties and File Types

Input/output also depends upon the procedures that manipulate files and the functions that return information about them.

Table 3-1 “Categories of Input/Output Routines ” categorizes the predefined input/output routines two ways: by purpose (for example, input or output) and by I/O type (sequential, textfile, or direct).

Table 3-1 Categories of Input/Output Routines

	Sequential I/O	Textfile I/O	Direct I/O
Opening Procedures	`reset` `rewrite` `append`	`reset` `rewrite` `append`	`open`
Input Procedures	`get` `read`	`get` `read` `readln`	`get` `read` `readdir`
Output Procedures	`put` `write`	`put` `write` `writeln` `page` `prompt` `overprint`	`put` `write` `writedir`
Positioning Procedure	None	None	`seek`
Association Procedures	`associate` `disassociate`	`associate` `disassociate`	`associate` `disassociate`
Status Functions	`eof` `position`	`eof` `eoln` `linepos`	`eof` `lastpos` `maxpos` `position`
Closing Procedure	`close`	`close`	`close`

Introduction

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