File input/output

 

C

Compiler support

Language

Headers

Type support

Program utilities

Variadic function support

Error handling

Dynamic memory management

Strings library

Algorithms

Numerics

Date and time utilities

Input/output support

Localization support

Concurrency support (C11)

Technical Specifications

Symbol index

 

File input/output

Types and objects
stdinstdoutstderr          FILE fpos_t
Functions File access fopenfopen_s (C11) freopenfreopen_s (C11)   fwide (C95) setbuf setvbuf fclose fflush Unformatted input/output fgetc fgets fputc fputs getchar getsgets_s (until C11)(C11) putchar puts ungetc fgetwcgetwc (C95)(C95) fgetws (C95) fputwcputwc (C95)(C95) fputws (C95) getwchar (C95) putwchar (C95) ungetwc (C95) Formatted input scanffscanfsscanfscanf_sfscanf_ssscanf_s (C11)(C11)(C11) wscanffwscanfswscanfwscanf_sfwscanf_sswscanf_s (C95)(C95)(C95)(C11)(C11)(C11) vscanfvfscanfvsscanfvscanf_svfscanf_svsscanf_s (C99)(C99)(C99)(C11)(C11)(C11) vwscanfvfwscanfvswscanfvwscanf_svfwscanf_svswscanf_s (C99)(C99)(C99)(C11)(C11)(C11)	Direct input/output fread fwrite Formatted output printffprintfsprintfsnprintfprintf_sfprintf_ssprintf_ssnprintf_s (C99)(C11)(C11)(C11)(C11) wprintffwprintfswprintfwprintf_sfwprintf_sswprintf_ssnwprintf_s (C95)(C95)(C95)(C11)(C11)(C11)(C11)   vprintfvfprintfvsprintfvsnprintfvprintf_svfprintf_svsprintf_svsnprintf_s (C99)(C11)(C11)(C11)(C11) vwprintfvfwprintfvswprintfvwprintf_svfwprintf_svswprintf_svsnwprintf_s (C95)(C95)(C95)(C11)(C11)(C11)(C11) File positioning ftell fgetpos fseek fsetpos rewind Error handling clearerr feof ferror perror Operations on files remove tmpfiletmpfile_s (C11) rename tmpnamtmpnam_s (C11)

 

The <stdio.h> header provides generic file operation support and supplies functions with narrow character input/output capabilities.

The <wchar.h> header supplies functions with wide character input/output capabilities.

I/O streams are denoted by objects of type FILE that can only be accessed and manipulated through pointers of type FILE*. Each stream is associated with an external physical device (file, standard input stream, printer, serial port, etc).

Types

Defined in header <stdio.h>
FILE	object type, capable of holding all information needed to control a C I/O stream (typedef)
fpos_t	non-array complete object type, capable of uniquely specifying a position and multibyte parser state in a file (typedef)

Predefined standard streams

Defined in header <stdio.h>
stdinstdoutstderr	expression of type FILE* associated with the input stream expression of type FILE* associated with the output stream expression of type FILE* associated with the error output stream (macro constant)

Functions

File access
Defined in header <stdio.h>
fopenfopen_s (C11)	opens a file (function)
freopenfreopen_s (C11)	open an existing stream with a different name (function)
fclose	closes a file (function)
fflush	synchronizes an output stream with the actual file (function)
setbuf	sets the buffer for a file stream (function)
setvbuf	sets the buffer and its size for a file stream (function)
Defined in header <wchar.h>
fwide (C95)	switches a file stream between wide character I/O and narrow character I/O (function)
Direct input/output
Defined in header <stdio.h>
fread	reads from a file (function)
fwrite	writes to a file (function)
Unformatted input/output
Narrow character
Defined in header <stdio.h>
fgetcgetc	gets a character from a file stream (function)
fgets	gets a character string from a file stream (function)
fputcputc	writes a character to a file stream (function)
fputs	writes a character string to a file stream (function)
getchar	reads a character from stdin (function)
getsgets_s (removed in C11)(C11)	reads a character string from stdin (function)
putchar	writes a character to stdout (function)
puts	writes a character string to stdout (function)
ungetc	puts a character back into a file stream (function)
Wide character
Defined in header <wchar.h>
fgetwcgetwc (C95)	gets a wide character from a file stream (function)
fgetws (C95)	gets a wide string from a file stream (function)
fputwcputwc (C95)	writes a wide character to a file stream (function)
fputws (C95)	writes a wide string to a file stream (function)
getwchar (C95)	reads a wide character from stdin (function)
putwchar (C95)	writes a wide character to stdout (function)
ungetwc (C95)	puts a wide character back into a file stream (function)
Formatted input/output
Narrow character
Defined in header <stdio.h>
scanffscanfsscanfscanf_sfscanf_ssscanf_s (C11)(C11)(C11)	reads formatted input from stdin, a file stream or a buffer (function)
vscanfvfscanfvsscanfvscanf_svfscanf_svsscanf_s (C99)(C99)(C99)(C11)(C11)(C11)	reads formatted input from stdin, a file stream or a buffer using variable argument list (function)
printffprintfsprintfsnprintfprintf_sfprintf_ssprintf_ssnprintf_s (C99)(C11)(C11)(C11)(C11)	prints formatted output to stdout, a file stream or a buffer (function)
vprintfvfprintfvsprintfvsnprintfvprintf_svfprintf_svsprintf_svsnprintf_s (C99)(C11)(C11)(C11)(C11)	prints formatted output to stdout, a file stream or a buffer using variable argument list (function)
Wide character
Defined in header <wchar.h>
wscanffwscanfswscanfwscanf_sfwscanf_sswscanf_s (C95)(C95)(C95)(C11)(C11)(C11)	reads formatted wide character input from stdin, a file stream or a buffer (function)
vwscanfvfwscanfvswscanfvwscanf_svfwscanf_svswscanf_s (C99)(C99)(C99)(C11)(C11)(C11)	reads formatted wide character input from stdin, a file stream or a buffer using variable argument list (function)
wprintffwprintfswprintfwprintf_sfwprintf_sswprintf_ssnwprintf_s (C95)(C95)(C95)(C11)(C11)(C11)(C11)	prints formatted wide character output to stdout, a file stream or a buffer (function)
vwprintfvfwprintfvswprintfvwprintf_svfwprintf_svswprintf_svsnwprintf_s (C95)(C95)(C95)(C11)(C11)(C11)(C11)	prints formatted wide character output to stdout, a file stream or a buffer using variable argument list (function)
File positioning
Defined in header <stdio.h>
ftell	returns the current file position indicator (function)
fgetpos	gets the file position indicator (function)
fseek	moves the file position indicator to a specific location in a file (function)
fsetpos	moves the file position indicator to a specific location in a file (function)
rewind	moves the file position indicator to the beginning in a file (function)
Error handling
Defined in header <stdio.h>
clearerr	clears errors (function)
feof	checks for the end-of-file (function)
ferror	checks for a file error (function)
perror	displays a character string corresponding of the current error to stderr (function)
Operations on files
Defined in header <stdio.h>
remove	erases a file (function)
rename	renames a file (function)
tmpfiletmpfile_s (C11)	returns a pointer to a temporary file (function)
tmpnamtmpnam_s (C11)	returns a unique filename (function)

Macro constants

Defined in header <stdio.h>
EOF	integer constant expression of type int and negative value (macro constant)
FOPEN_MAX	maximum number of files that can be open simultaneously (macro constant)
FILENAME_MAX	size needed for an array of char to hold the longest supported file name (macro constant)

_PRINTF_NAN_LEN_MAX (C23)

the maximum number of characters output for any (possibly negated) NaN value (macro constant)

BUFSIZ	size of the buffer used by setbuf (macro constant)
_IOFBF_IOLBF_IONBF	indicates the buffering mode (fully buffered / line buffered / unbuffered) to be set by setvbuf (macro constant)
SEEK_SETSEEK_CURSEEK_END	indicates the offset origin (beginning / current position / end) to be used by fseek (macro constant)
TMP_MAXTMP_MAX_S (C11)	maximum number of unique filenames that can be generated by tmpnam / tmpnam_s (macro constant)
L_tmpnamL_tmpnam_s (C11)	size needed for an array of char to hold the result of tmpnam / tmpnam_s (macro constant)

References

• C23 standard (ISO/IEC 9899:2024):

• 7.21 Input/output <stdio.h> (p: TBD)

• 7.29 Extended multibyte and wide character utilities <wchar.h> (p: TBD)

• 7.31.11 Input/output <stdio.h> (p: TBD)

• 7.31.16 Extended multibyte and wide character utilities <wchar.h> (p: TBD)

• K.3.5 Input/output <stdio.h> (p: TBD)

• C17 standard (ISO/IEC 9899:2018):

• 7.21 Input/output <stdio.h> (p: TBD)

• 7.29 Extended multibyte and wide character utilities <wchar.h> (p: TBD)

• 7.31.11 Input/output <stdio.h> (p: TBD)

• 7.31.16 Extended multibyte and wide character utilities <wchar.h> (p: TBD)

• K.3.5 Input/output <stdio.h> (p: TBD)

• C11 standard (ISO/IEC 9899:2011):

• 7.21 Input/output <stdio.h> (p: 296-339)

• 7.29 Extended multibyte and wide character utilities <wchar.h> (p: 402-446)

• 7.31.11 Input/output <stdio.h> (p: 456)

• 7.31.16 Extended multibyte and wide character utilities <wchar.h> (p: 456)

• K.3.5 Input/output <stdio.h> (p: 586-603)

• C99 standard (ISO/IEC 9899:1999):

• 7.19 Input/output <stdio.h> (p: 262-305)

• 7.24 Extended multibyte and wide character utilities <wchar.h> (p: 348-392)

• 7.26.9 Input/output <stdio.h> (p: 402)

• 7.26.12 Extended multibyte and wide character utilities <wchar.h> (p: 402)

• C89/C90 standard (ISO/IEC 9899:1990):

• 4.9 INPUT/OUTPUT <stdio.h>

• 4.13.6 Input/output <stdio.h>

See also

C++ documentation for C-style file input/output