# C-style file input/output

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< cpp‎ | io

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 | 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 std::setbuf (macro constant)
_IOFBF_IOLBF_IONBF | argument to std::setbuf indicating fully buffered I/O argument to std::setbuf indicating line buffered I/O argument to std::setbuf indicating unbuffered I/O (macro constant)
SEEK_SETSEEK_CURSEEK_END | argument to std::fseek indicating seeking from beginning of the file argument to std::fseek indicating seeking from the current file position argument to std::fseek indicating seeking from end of the file (macro constant)
TMP_MAX | maximum number of unique filenames that is guaranteed to be generatable 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

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