Editing C file input/output (section)

==Overview==
This library uses what are called streams to operate with physical devices such as keyboards, printers, terminals or with any other type of files supported by the system. Streams are an abstraction to interact with these in a uniform way. All streams have similar properties independent of the individual characteristics of the physical media they are associated with.<ref>{{Cite web |title=(stdio.h) - C++ Reference |url=http://www.cplusplus.com/reference/cstdio/ |access-date=July 25, 2021 |website=C++ |language=en-US}}</ref>

===Functions===
Most of the C file input/output functions are defined in {{mono|<stdio.h>}} (or in the [[C++]] header {{mono|cstdio}}, which contains the standard C functionality but in the {{mono|std}} [[namespace]]).

{| class="wikitable"
|-
!
! Byte<br />character
! Wide<br />character
! Description
|-
! rowspan=9 | File access
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|fopen}}[https://en.cppreference.com/w/c/io/fopen fopen]
| Opens a file (with a non-Unicode filename on Windows and possible UTF-8 filename on Linux)
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|popen}}[https://man7.org/linux/man-pages/man3/popen.3.html popen]
| opens a process by creating a pipe, forking, and invoking the shell
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|freopen}}[https://en.cppreference.com/w/c/io/freopen freopen]
| Opens a different file with an existing stream
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|fflush}}[https://en.cppreference.com/w/c/io/fflush fflush]
| Synchronizes an output stream with the actual file
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|fclose}}[https://en.cppreference.com/w/c/io/fclose fclose]
| Closes a file
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|pclose}}[https://man7.org/linux/man-pages/man3/pclose.3p.html pclose]
| closes a stream
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|setbuf}}[https://en.cppreference.com/w/c/io/setbuf setbuf]
| Sets the buffer for a file stream
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|setvbuf}}[https://en.cppreference.com/w/c/io/setvbuf setvbuf]
| Sets the buffer and its size for a file stream
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|fwide}}[https://en.cppreference.com/w/c/io/fwide fwide]
| Switches a file stream between wide-character I/O and narrow-character I/O
|-
! rowspan=2 | Direct <br /> input/output
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|fread}}[https://en.cppreference.com/w/c/io/fread fread]
| Reads from a file
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|fwrite}}[https://en.cppreference.com/w/c/io/fwrite fwrite]
| Writes to a file
|-
! rowspan=9 | Unformatted <br /> input/output
| style="font-family:monospace" | {{anchor|fgetc|getc}}[https://en.cppreference.com/w/c/io/fgetc fgetc]<br />[https://en.cppreference.com/w/c/io/getc getc]
| style="font-family:monospace"| {{anchor|fgetwc|getwc}}[https://en.cppreference.com/w/c/io/fgetwc fgetwc]<br />[https://en.cppreference.com/w/c/io/getwc getwc]
| Reads a byte/{{mono|wchar_t}} from a file stream
|-
| style="font-family:monospace" | {{anchor|fgets}}[https://en.cppreference.com/w/c/io/fgets fgets]
| style="font-family:monospace" | {{anchor|fgetws}}[https://en.cppreference.com/w/c/io/fgetws fgetws]
| Reads a byte/{{mono|wchar_t}} line from a file stream
|-
| style="font-family:monospace" | {{anchor|fputc|putc}}[https://en.cppreference.com/w/c/io/fputc fputc]<br />[https://en.cppreference.com/w/c/io/putc putc]
| style="font-family:monospace" | {{anchor|fputwc|putwc}}[https://en.cppreference.com/w/c/io/fputwc fputwc]<br />[https://en.cppreference.com/w/c/io/putwc putwc]
| Writes a byte/{{mono|wchar_t}} to a file stream
|-
| style="font-family:monospace" | {{anchor|fputs}}[https://en.cppreference.com/w/c/io/fputs fputs]
| style="font-family:monospace" | {{anchor|fputws}}[https://en.cppreference.com/w/c/io/fputws fputws]
| Writes a byte/{{mono|wchar_t}} string to a file stream
|-
| style="font-family:monospace" | {{anchor|getchar}}[https://en.cppreference.com/w/c/io/getchar getchar]
| style="font-family:monospace" | {{anchor|getwchar}}[https://en.cppreference.com/w/c/io/getwchar getwchar]
| Reads a byte/{{mono|wchar_t}} from stdin
|-
| style="font-family:monospace" | {{anchor|gets}}<s>[https://en.cppreference.com/w/c/io/gets gets]</s>
| {{n/a}}
| Reads a byte string from stdin until a newline or end of file is encountered (deprecated in C99, removed from C11)
|-
| style="font-family:monospace" | {{anchor|putchar}}[https://en.cppreference.com/w/c/io/putchar putchar]
| style="font-family:monospace" | {{anchor|putwchar}}[https://en.cppreference.com/w/c/io/putwchar putwchar]
| Writes a byte/{{mono|wchar_t}} to stdout
|-
| style="font-family:monospace" | {{anchor|puts}}[https://en.cppreference.com/w/c/io/puts puts]
| {{n/a}}
| Writes a byte string to stdout
|-
| style="font-family:monospace" | {{anchor|ungetc}}[https://en.cppreference.com/w/c/io/ungetc ungetc]
| style="font-family:monospace" | {{anchor|ungetwc}}[https://en.cppreference.com/w/c/io/ungetwc ungetwc]
| Puts a byte/{{mono|wchar_t}} back into a file stream
|-
! rowspan=5 | Formatted <br /> input/output
| style="font-family:monospace" | {{anchor|scanf|fscanf|sscanf}}[https://en.cppreference.com/w/c/io/scanf scanf]<br />[https://en.cppreference.com/w/c/io/fscanf fscanf]<br />[https://en.cppreference.com/w/c/io/sscanf sscanf]
| style="font-family:monospace" | {{anchor|wscanf|fwscanf|swscanf}}[https://en.cppreference.com/w/c/io/wscanf wscanf]<br />[https://en.cppreference.com/w/c/io/fwscanf fwscanf]<br />[https://en.cppreference.com/w/c/io/swscanf swscanf]
| Reads formatted byte/{{mono|wchar_t}} input from stdin,<br />a file stream or a buffer
|-
| style="font-family:monospace" | {{anchor|vscanf|vfscanf|vsscanf}}[https://en.cppreference.com/w/c/io/vscanf vscanf]<br />[https://en.cppreference.com/w/c/io/vfscanf vfscanf]<br />[https://en.cppreference.com/w/c/io/vsscanf vsscanf]
| style="font-family:monospace" | {{anchor|vwscanf|vfwscanf|vswscanf}}[https://en.cppreference.com/w/c/io/vwscanf vwscanf]<br />[https://en.cppreference.com/w/c/io/vfwscanf vfwscanf]<br />[https://en.cppreference.com/w/c/io/vswscanf vswscanf]
| Reads formatted input byte/{{mono|wchar_t}} from stdin,<br />a file stream or a buffer using variable argument list
|-
| style="font-family:monospace" | {{anchor|printf|fprintf|sprintf|snprintf}}[https://en.cppreference.com/w/c/io/printf printf]<br />[https://en.cppreference.com/w/c/io/fprintf fprintf]<br />[https://en.cppreference.com/w/c/io/sprintf sprintf]<br />[https://en.cppreference.com/w/c/io/snprintf snprintf]
| style="font-family:monospace" | {{anchor|wprintf|fwprintf|swprintf}}[https://en.cppreference.com/w/c/io/wprintf wprintf]<br />[https://en.cppreference.com/w/c/io/fwprintf fwprintf]<br />[https://en.cppreference.com/w/c/io/swprintf swprintf]
| Prints formatted byte/{{mono|wchar_t}} output to stdout,<br />a file stream or a buffer
|-
| style="font-family:monospace" | {{anchor|vprintf|vfprintf|vsprintf|vsnprintf}}[https://en.cppreference.com/w/c/io/vprintf vprintf]<br />[https://en.cppreference.com/w/c/io/vfprintf vfprintf]<br />[https://en.cppreference.com/w/c/io/vsprintf vsprintf]<br />[https://en.cppreference.com/w/c/io/vsnprintf vsnprintf]
| style="font-family:monospace" | {{anchor|vwprintf|vfwprintf|vswprintf}}[https://en.cppreference.com/w/c/io/vwprintf vwprintf]<br />[https://en.cppreference.com/w/c/io/vfwprintf vfwprintf]<br />[https://en.cppreference.com/w/c/io/vfwprintf vswprintf]
| Prints formatted byte/{{mono|wchar_t}} output to stdout,<br />a file stream, or a buffer using variable argument list
|-
| style="font-family:monospace" | {{anchor|perror}}[https://en.cppreference.com/w/c/io/perror perror]
| {{n/a}}
| Writes a description of the [[errno.h|current error]] to stderr
|-
! rowspan=5 | File positioning
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|ftell}}[https://en.cppreference.com/w/c/io/ftell ftell]<br/>ftello
| Returns the current file position indicator
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|fseek}}[https://en.cppreference.com/w/c/io/fseek fseek]<br/>fseeko
| Moves the file position indicator to a specific location in a file
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|fgetpos}}[https://en.cppreference.com/w/c/io/fgetpos fgetpos]
| Gets the file position indicator
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|fsetpos}}[https://en.cppreference.com/w/c/io/fsetpos fsetpos]
| Moves the file position indicator to a specific location in a file
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|rewind}}[https://en.cppreference.com/w/c/io/rewind rewind]
| Moves the file position indicator to the beginning in a file
|-
! rowspan=3 | Error<br />handling
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|clearerr}}[https://en.cppreference.com/w/c/io/clearerr clearerr]
| Clears errors
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|feof}}[https://en.cppreference.com/w/c/io/feof feof]
| Checks for the end-of-file
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|ferror}}[https://en.cppreference.com/w/c/io/ferror ferror]
| Checks for a file error
|-
! rowspan=4 | Operations <br />on files
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|remove}}[https://en.cppreference.com/w/c/io/remove remove]
| Erases a file
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|rename}}[https://en.cppreference.com/w/c/io/rename rename]
| [[rename (computing)|Rename]]s a file
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|tmpfile}}[https://en.cppreference.com/w/c/io/tmpfile tmpfile]
| Returns a pointer to a temporary file
|-
| colspan=2 style="text-align:center;font-family:monospace" | {{anchor|tmpnam}}[https://en.cppreference.com/w/c/io/tmpnam tmpnam]
| Returns a unique filename
|}

===Constants===
Constants defined in the {{mono|<stdio.h>}} header include:

{| class="wikitable"
|-
! Name !! Notes
|-
! style="font-family:monospace" | [[End-of-file|EOF]]
| A negative integer of type {{mono|int}} used to indicate end-of-file conditions
|-
! style="font-family:monospace" | {{Anchor|BUFSIZ}} [http://c-p-p.net/c/stdio.h/bufsiz BUFSIZ]
| An integer which is the size of the buffer used by the {{mono|setbuf()}} function
|-
! style="font-family:monospace" | FILENAME_MAX
| The size of a {{mono|char}} array which is large enough to store the name of any file that can be opened
|-
! style="font-family:monospace" | FOPEN_MAX
| The number of files that may be open simultaneously; will be at least eight
|-
! style="font-family:monospace" | _IOFBF
| An abbreviation for "input/output fully buffered"; it is an integer which may be passed to the {{mono|setvbuf()}} function to request ''block buffered'' input and output for an open stream
|-
! style="font-family:monospace" | _IOLBF
| An abbreviation for "input/output line buffered"; it is an integer which may be passed to the {{mono|setvbuf()}} function to request ''line buffered'' input and output for an open stream
|-
! style="font-family:monospace" | _IONBF
| An abbreviation for "input/output not buffered"; it is an integer which may be passed to the {{mono|setvbuf()}} function to request ''unbuffered'' input and output for an open stream
|-
! style="font-family:monospace" | L_tmpnam
| The size of a {{mono|char}} array which is large enough to store a temporary filename generated by the {{mono|tmpnam()}} function
|-
! style="font-family:monospace" | NULL
| A macro expanding to the [[null pointer]] constant; that is, a constant representing a pointer value which is guaranteed '''not''' to be a valid address of an object in memory
|-
! style="font-family:monospace" | SEEK_CUR
| An integer which may be passed to the {{mono|fseek()}} function to request positioning relative to the current file position
|-
! style="font-family:monospace" | SEEK_END
| An integer which may be passed to the {{mono|fseek()}} function to request positioning relative to the end of the file
|-
! style="font-family:monospace" | SEEK_SET
| An integer which may be passed to the {{mono|fseek()}} function to request positioning relative to the beginning of the file
|-
! style="font-family:monospace" | TMP_MAX
| The maximum number of unique filenames generable by the {{mono|tmpnam()}} function; will be at least 25
|}

===Variables===
[[File:Stdstreams-notitle.svg|frameless|right]]
Variables defined in the {{mono|<stdio.h>}} header include:

{| class="wikitable"
|-
! Name !! Notes
|-
! style="font-family:monospace" | [[Standard streams#Standard input (stdin)|stdin]]
| A pointer to a {{mono|FILE}} which refers to the standard input stream, usually a keyboard.
|-
! style="font-family:monospace" | [[Standard streams#Standard output (stdout)|stdout]]
| A pointer to a {{mono|FILE}} which refers to the standard output stream, usually a display terminal.
|-
! style="font-family:monospace" | [[Standard streams#Standard error (stderr)|stderr]]
| A pointer to a {{mono|FILE}} which refers to the standard error stream, often a display terminal.
|}

===Member types===
Data types defined in the {{mono|<stdio.h>}} header include:
*{{mono|[https://en.cppreference.com/w/c/io FILE]}} – also known as a {{anchor|file handle}}'''file [[Handle (computing)|handle]]''' or a '''{{Visible anchor|FILE pointer}}''', this is an [[opaque pointer]] containing the information about a file or text stream needed to perform input or output operations on it, including:
**platform-specific identifier of the associated I/O device, such as a [[file descriptor]] 
**the buffer
**stream orientation indicator (unset, narrow, or wide)
**stream buffering state indicator (unbuffered, line buffered, fully buffered)
**I/O mode indicator (input stream, output stream, or update stream)
**binary/text mode indicator
**end-of-file indicator
**error indicator
**the current stream position and multibyte conversion state (an object of type mbstate_t)
**reentrant lock (required as of [[C11 (C standard revision)|C11]])
*{{mono|fpos_t}} – a non-array type capable of uniquely identifying the position of every byte in a file and every conversion state that can occur in all supported multibyte character encodings
*{{mono|size_t}} – an [[unsigned integer]] type which is the type of the result of the {{mono|[[sizeof]]}} operator.

===Extensions{{anchor|POSIX}}===
The [[POSIX]] standard defines several extensions to {{mono|stdio}} in its Base Definitions, among which are a {{mono|readline}} function that allocates memory, the {{mono|fileno}} and {{mono|fdopen}} functions that establish the link between {{mono|FILE}} objects and [[file descriptor]]s, and a group of functions for creating {{mono|FILE}} objects that refer to in-memory buffers.<ref>{{man|bd|stdio.h|SUS}}</ref>