End - of - file - wikipedia End - of - file In computing, end - of - file ( commonly abbreviated EOF ) is a condition in a computer operating system where no more data can be read from a data source. The data source is usually called a file or stream. In the C Standard Library, the character reading functions such as getchar 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 ( but is commonly - 1, such as in glibc ) and is distinct from all valid character codes. 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 or dedicated function, such as ferror is often required to determine which ). EOF character This section relies largely or entirely on a single source. Relevant discussion may be found on the talk page. Please help improve this article by introducing citations to additional sources. ( March 2015 ) 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 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 ). AmigaDOS is similar but uses Control - instead of Control - D. In Microsoft 's DOS and Windows ( and in CP / M and many DEC operating systems ), 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 Control - Z, code 26. Some MS - DOS programs, including parts of the Microsoft MS - DOS shell ( COMMAND.COM ) 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 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 MS - DOS filesystem has always recorded the exact byte - length of files, so this was never necessary on MS - 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 reflective strip that was used to announce impending physical end of tape was also called an EOT marker. See also Computer science portal End - of - transmission character Substitute character End of message Here document References Jump up ^ Wayne Pollock. `` Shell Here Document Overview ''. hccfl.edu. Archived from the original on 2014 - 05 - 29. Retrieved 2014 - 05 - 28. Jump up ^ https://www.gnu.org/software/libc/manual/html_mono/libc.html#EOF-and-Errors Jump up ^ https://www.loc.gov/marc/specifications/specexchtape2.html#mark Retrieved from `` https://en.wikipedia.org/w/index.php?title=End-of-file&oldid=847561126 '' Categories : C standard library Computer files Hidden categories : Articles needing additional references from March 2015 All articles needing additional references Talk About Wikipedia Azərbaycanca Български Català Deutsch Español Français 한국어 עברית 日本 語 Polski Português Русский Српски / srpski Svenska Українська 中文 7 more Edit links This page was last edited on 26 June 2018, at 06 : 54 ( UTC ). Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: what is the actual decimal numeric value of the symbol eof
Answer: implementation-dependent (but is commonly -1, such as in glibc[2])