computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...

, end-of-file (EOF) is a condition in a computer

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...

where no more data can be read from a data source. The data source is usually called a

file File or filing may refer to: Mechanical tools and processes * File (tool), a tool used to ''remove'' fine amounts of material from a workpiece **Filing (metalworking), a material removal process in manufacturing ** Nail file, a tool used to gent ...

or stream.

Details

In the C standard library, the character reading functions such as

getchar The C programming language provides many standard library functions for file input and output. These functions make up the bulk of the C standard library header . The functionality descends from a "portable I/O package" written by Mike Lesk at ...

return a value equal to the symbolic value (macro) EOF to indicate that an end-of-file condition has occurred. The actual value of EOF is implementation-dependent and must be negative (but is commonly −1, such as in

glibc The GNU C Library, commonly known as glibc, is the GNU Project's implementation of the C standard library. Despite its name, it now also directly supports C++ (and, indirectly, other programming languages). It was started in the 1980s by ...

). Block-reading functions return the number of bytes read, and if this is fewer than asked for, then the end of file was reached or an error occurred (checking of

errno 


errno.h is a header file in the standard library of the C programming language. It defines  macros for reporting and retrieving error conditions using the symbol errno (short for "error number").International Standard for Programming Language C ( ...

or dedicated function, such as ferror is required to determine which).

EOF character

Input from a terminal never really "ends" (unless the device is disconnected), but it is useful to enter more than one "file" into a terminal, so a key sequence is reserved to indicate end of input. In

UNIX Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...

the translation of the keystroke to EOF is performed by the terminal driver, so a program does not need to distinguish terminals from other input files. By default, the driver converts a Control-D character at the start of a line into an end-of-file indicator. To insert an actual Control-D (ASCII 04) character into the input stream, the user precedes it with a "quote" command character (usually

Control-V In computing, Control-V is a key stroke with a variety of uses including generation of a control character in ASCII code, also known as the synchronous idle ( SYN) character. The key stroke is generated by pressing the key while holding down the ...

). AmigaDOS is similar but uses Control-\ instead of Control-D. In

DOS DOS is shorthand for the MS-DOS and IBM PC DOS family of operating systems. DOS may also refer to: Computing * Data over signalling (DoS), multiplexing data onto a signalling channel * Denial-of-service attack (DoS), an attack on a communicat ...

and

Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ser ...

(and in CP/M and many DEC operating systems such as the

PDP-6 The PDP-6, short for Programmed Data Processor model 6, is a computer developed by Digital Equipment Corporation (DEC) during 1963 and first delivered in the summer of 1964. It was an expansion of DEC's existing 18-bit systems to use a 36-bit d ...

monitor,

RT-11 RT-11 (Real-time 11) is a discontinued small, low-end, single-user real-time operating system for the full line of Digital Equipment Corporation PDP-11 16-bit computers. RT-11 was first implemented in 1970. It was widely used for real-time computin ...

, VMS or

TOPS-10 TOPS-10 System (''Timesharing / Total Operating System-10'') is a discontinued operating system from Digital Equipment Corporation (DEC) for the PDP-10 (or DECsystem-10) mainframe computer family. Launched in 1967, TOPS-10 evolved from the earlie ...

), reading from the terminal will never produce an EOF. Instead, programs recognize that the source is a terminal (or other "character device") and interpret a given reserved character or sequence as an end-of-file indicator; most commonly this is an

ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because ...

Control-Z In computer data, a substitute character (␚) is a control character that is used to pad transmitted data in order to send it in blocks of fixed size, or to stand in place of a character that is recognized to be invalid, erroneous or unreprese ...

, code 26. Some MS-DOS programs, including parts of the Microsoft MS-DOS shell (

COMMAND.COM COMMAND.COM is the default command-line interpreter for MS-DOS, Windows 95, Windows 98 and Windows Me. In the case of DOS, it is the default user interface as well. It has an additional role as the usual first program run after boot (init proc ...

) and operating-system utility programs (such as EDLIN), treat a Control-Z in a text file as marking the end of meaningful data, and/or append a Control-Z to the end when writing a text file. This was done for two reasons: * Backward compatibility with CP/M. The CP/M file system (and also the original

8-bit FAT In computer architecture, 8-bit integers or other data units are those that are 8 bits wide (1 octet). Also, 8-bit central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers or data buses ...

implemented in

Microsoft BASIC Microsoft BASIC is the foundation software product of the Microsoft company and evolved into a line of BASIC interpreters and compiler(s) adapted for many different microcomputers. It first appeared in 1975 as Altair BASIC, which was the first ...

) only recorded the lengths of files in multiples of 128-byte "records", so by convention a Control-Z character was used to mark the end of meaningful data if it ended in the middle of a record. The

FAT12 File Allocation Table (FAT) is a file system developed for personal computers. Originally developed in 1977 for use on floppy disks, it was adapted for use on hard disks and other devices. It is often supported for compatibility reasons by ...

filesystem introduced with 86-DOS and MS-DOS has always recorded the exact byte-length of files, so this was never necessary on DOS. * It allows programs to use the same code to read input from both a terminal and a text file. In the ANSI X3.27-1969 magnetic tape standard, the end of file was indicated by a tape mark, which consisted of a gap of approximately 3.5 inches of tape followed by a single byte containing the character 13 (hex) for nine-track tapes and 17 (octal) for seven-track tapes. The end-of-tape, commonly abbreviated as EOT, was indicated by two tape marks. This was the standard used, for example, on

IBM 360 The IBM System/360 (S/360) is a family of mainframe computer systems that was announced by IBM on April 7, 1964, and delivered between 1965 and 1978. It was the first family of computers designed to cover both commercial and scientific applica ...

. The reflective strip that was used to announce impending physical end of tape was also called an EOT marker.

References

{{reflist, refs= {{cite web , title=Shell Here Document Overview , publisher=hccfl.edu , author-first=Wayne , author-last=Pollock , url=http://content.hccfl.edu/pollock/ShScript/HereDoc.htm , access-date=2014-05-28 , url-status=dead , archive-url=https://web.archive.org/web/20140529084958/http://content.hccfl.edu/pollock/ShScript/HereDoc.htm , archive-date=2014-05-29 {{cite web , title=The GNU C Library , website=www.gnu.org , url=https://www.gnu.org/software/libc/manual/html_mono/libc.html#EOF-and-Errors {{cite book , title=PDP-6 Multiprogramming System Manual , chapter=Table of IO Device Characteristics - Console or Teletypewriters , id=DEC-6-0-EX-SYS-UM-IP-PRE00 , publisher=

Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president un ...

(DEC) , publication-place=Maynard, Massachusetts, USA , date=1965 , page=43 , url=http://bitsavers.trailing-edge.com/pdf/dec/pdp6/DEC-6-0-EX-SYS-UM-IP-PRE00_Multiprogramming_System_Manual_1965.pdf , access-date=2014-07-10 , url-status=live , archive-url=https://web.archive.org/web/20140714140253/http://bitsavers.trailing-edge.com/pdf/dec/pdp6/DEC-6-0-EX-SYS-UM-IP-PRE00_Multiprogramming_System_Manual_1965.pdf , archive-date=2014-07-14 (1+84+10 pages) {{cite book , title=PDP-10 Reference Handbook: Communicating with the Monitor - Time-Sharing Monitors , volume=3 , chapter=5.1.1.1. Device Dependent Functions - Data Modes - Full-Duplex Software A(ASCII) and AL(ASCII Line) , publisher=

(DEC) , date=1969 , pages=5-3 – 5-6 -5 (431), url=http://bitsavers.org/pdf/dec/pdp10/1970_PDP-10_Ref/1970PDP10Ref_Part3.pdf , access-date=2014-07-10 , url-status=live , archive-url=https://web.archive.org/web/20111115083418/http://www.bitsavers.org/pdf/dec/pdp10/1970_PDP-10_Ref/1970PDP10Ref_Part3.pdf , archive-date=2011-11-15 (207 pages) {{cite web , title=Tape Transfer (Pre-1977): Exchange Media: MARC 21 Specifications for Record Structure, Character Sets, and Exchange Media (Library of Congress) , website=www.loc.gov , url=https://www.loc.gov/marc/specifications/specexchtape2.html#mark C standard library Computer files

Details

EOF character

See also

References