C-style file input/output

The C I/O subset of the C++ standard library implements C-style stream input/output operations. The <cstdio> header provides generic file operation support and supplies functions with narrow and multibyte character input/output capabilities, and the <cwchar> header provides functions with wide character input/output capabilities.

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

Types

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

Predefined standard streams

Defined in header <cstdio>
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

Defined in header <cstdio>
File access
fopen	opens a file (function)
freopen	open an existing stream with a different name (function)
fclose	closes a file (function)
fflush	synchronizes an output stream with the actual file (function)
fwide	switches a file stream between wide character I/O and narrow character I/O (function)
setbuf	sets the buffer for a file stream (function)
setvbuf	sets the buffer and its size for a file stream (function)
Direct input/output
fread	reads from a file (function)
fwrite	writes to a file (function)
Unformatted input/output
Byte/multibyte character
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)
gets (deprecated in C++11)(removed in C++14)	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
fgetwcgetwc	gets a wide character from a file stream (function)
fgetws	gets a wide string from a file stream (function)
fputwcputwc	writes a wide character to a file stream (function)
fputws	writes a wide string to a file stream (function)
getwchar	reads a wide character from stdin (function)
putwchar	writes a wide character to stdout (function)
ungetwc	puts a wide character back into a file stream (function)
Formatted input/output
Byte/multibyte character
scanffscanfsscanf	reads formatted input from stdin, a file stream or a buffer (function)
vscanfvfscanfvsscanf (C++11)(C++11)(C++11)	reads formatted input from stdin, a file stream or a buffer using variable argument list (function)
printffprintfsprintfsnprintf (C++11)	prints formatted output to stdout, a file stream or a buffer (function)
vprintfvfprintfvsprintfvsnprintf (C++11)	prints formatted output to stdout, a file stream or a buffer using variable argument list (function)
Wide character
wscanffwscanfswscanf	reads formatted wide character input from stdin, a file stream or a buffer (function)
vwscanfvfwscanfvswscanf (C++11)(C++11)(C++11)	reads formatted wide character input from stdin, a file stream or a buffer using variable argument list (function)
wprintffwprintfswprintf	prints formatted wide character output to stdout, a file stream or a buffer (function)
vwprintfvfwprintfvswprintf	prints formatted wide character output to stdout, a file stream or a buffer using variable argument list (function)
File positioning
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
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
remove	erases a file (function)
rename	renames a file (function)
tmpfile	creates and opens a temporary, auto-removing file (function)
tmpnam	returns a unique filename (function)

Macro constants

Defined in header <cstdio>
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 (C++26)

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

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

See also

C documentation for File input/output