# File input/output

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< c

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>`
stdin stdout stderr | 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>`
fopen fopen_s (C11) | opens a file (function)
freopen freopen_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>`
fgetc getc | gets a character from a file stream (function)
fgets | gets a character string from a file stream (function)
fputc putc | 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)
gets gets_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>`
fgetwc getwc (C95) | gets a wide character from a file stream (function)
fgetws (C95) | gets a wide string from a file stream (function)
fputwc putwc (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>`
scanf fscanf sscanf scanf_s fscanf_s sscanf_s (C11)(C11)(C11) | reads formatted input from stdin, a file stream or a buffer (function)
vscanf vfscanf vsscanf vscanf_s vfscanf_s vsscanf_s (C99)(C99)(C99)(C11)(C11)(C11) | reads formatted input from stdin, a file stream or a buffer using variable argument list (function)
printf fprintf sprintf snprintf printf_s fprintf_s sprintf_s snprintf_s (C99)(C11)(C11)(C11)(C11) | prints formatted output to stdout, a file stream or a buffer (function)
vprintf vfprintf vsprintf vsnprintf vprintf_s vfprintf_s vsprintf_s vsnprintf_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>`
wscanf fwscanf swscanf wscanf_s fwscanf_s swscanf_s (C95)(C95)(C95)(C11)(C11)(C11) | reads formatted wide character input from stdin, a file stream or a buffer (function)
vwscanf vfwscanf vswscanf vwscanf_s vfwscanf_s vswscanf_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)
wprintf fwprintf swprintf wprintf_s fwprintf_s swprintf_s snwprintf_s (C95)(C95)(C95)(C11)(C11)(C11)(C11) | prints formatted wide character output to stdout, a file stream or a buffer (function)
vwprintf vfwprintf vswprintf vwprintf_s vfwprintf_s vswprintf_s vsnwprintf_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)
tmpfile tmpfile_s (C11) | returns a pointer to a temporary file (function)
tmpnam tmpnam_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)
BUFSIZ | size of the buffer used by setbuf (macro constant)
_IOFBF_IOLBF_IONBF | argument to setvbuf indicating fully buffered I/O argument to setvbuf indicating line buffered I/O argument to setvbuf indicating unbuffered I/O (macro constant)
SEEK_SET SEEK_CUR SEEK_END | argument to fseek indicating seeking from beginning of the file argument to fseek indicating seeking from the current file position argument to fseek indicating seeking from end of the file (macro constant)
TMP_MAX TMP_MAX_S (C11) | maximum number of unique filenames that can be generated by tmpnam maximum number of unique filenames that can be generated by tmpnam_s (macro constant)
L_tmpnam L_tmpnam_s (C11) | size needed for an array of char to hold the result of tmpnam size needed for an array of char to hold the result of tmpnam_s (macro constant)

### References

- C23 standard (ISO/IEC 9899:2023):

  - 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

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