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# C-style file input/output

From cppreference.com
< 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 objects of type std::FILE that can only be accessed and manipulated through pointers of type std::FILE* (Note: while it may be possible to create a local object of type std::FILE by dereferencing and copying a valid std::FILE*, using the address of such copy in the I/O functions is undefined behavior). Each C stream is associated with an external physical device (file, standard input stream, printer, serial port, etc).

C streams can be used for both unformatted and formatted input and output. They are locale-sensitive and may perform wide/multibyte conversions as necessary. Unlike C++ streams, where each stream is associated with its own locale, all C streams access the same locale object: the one most recently installed with std::setlocale.

Besides the system-specific information necessary to access the device (e.g. a POSIX file descriptor), each C stream object holds the following:

1) Character width: narrow or wide
2) Buffering state: unbuffered, line-buffered, fully buffered.
3) The buffer, which may be replaced by an external, user-provided buffer.
4) I/O mode: input, output, or update (both input and output).
5) Binary/text mode indicator.
6) End-of-file status indicator.
7) Error status indicator.
8) File position indicator (an object of type std::fpos_t), which, for wide character streams, includes the parse state (an object of type std::mbstate_t).

### [edit] Functions

##### File access
fopen | opens a file (function) [edit]
freopen | open an existing stream with a different name (function) [edit]
fclose | closes a file (function) [edit]
fflush | synchronizes an output stream with the actual file (function) [edit]
fwide | switches a file stream between wide character I/O and narrow character I/O (function) [edit]
setbuf | sets the buffer for a file stream (function) [edit]
setvbuf | sets the buffer and its size for a file stream (function) [edit]
##### Direct input/output
fread | reads from a file (function) [edit]
fwrite | writes to a file (function) [edit]
##### Unformatted input/output
##### Narrow character
fgetcgetc | gets a character from a file stream (function) [edit]
fgets | gets a character string from a file stream (function) [edit]
fputcputc | writes a character to a file stream (function) [edit]
fputs | writes a character string to a file stream (function) [edit]
getchar | reads a character from stdin (function) [edit]
gets | reads a character string from stdin(until C++14) (function) [edit]
putchar | writes a character to stdout (function) [edit]
puts | writes a character string to stdout (function) [edit]
ungetc | puts a character back into a file stream (function) [edit]
##### Wide character
fgetwcgetwc | gets a wide character from a file stream (function) [edit]
fgetws | gets a wide string from a file stream (function) [edit]
fputwcputwc | writes a wide character to a file stream (function) [edit]
fputws | writes a wide string to a file stream (function) [edit]
getwchar | reads a wide character from stdin (function) [edit]
putwchar | writes a wide character to stdout (function) [edit]
ungetwc | puts a wide character back into a file stream (function) [edit]
##### Formatted input/output
##### Narrow/multibyte character
scanffscanfsscanf | reads formatted input from stdin, a file stream or a buffer (function) [edit]
vscanfvfscanfvsscanf (C++11)(C++11)(C++11) | reads formatted input from stdin, a file stream or a buffer using variable argument list (function) [edit]
printffprintfsprintfsnprintf (C++11) | prints formatted output to stdout, a file stream or a buffer (function) [edit]
vprintfvfprintfvsprintfvsnprintf (C++11) | prints formatted output to stdout, a file stream or a buffer using variable argument list (function) [edit]
##### Wide character
wscanffwscanfswscanf | reads formatted wide character input from stdin, a file stream or a buffer (function) [edit]
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) [edit]
wprintffwprintfswprintf | prints formatted wide character output to stdout, a file stream or a buffer (function) [edit]
vwprintfvfwprintfvswprintf | prints formatted wide character output to stdout, a file stream or a buffer using variable argument list (function) [edit]
##### File positioning
ftell | returns the current file position indicator (function) [edit]
fgetpos | gets the file position indicator (function) [edit]
fseek | moves the file position indicator to a specific location in a file (function) [edit]
fsetpos | moves the file position indicator to a specific location in a file (function) [edit]
rewind | moves the file position indicator to the beginning in a file (function) [edit]
##### Error handling
clearerr | clears errors (function) [edit]
feof | checks for the end-of-file (function) [edit]
ferror | checks for a file error (function) [edit]
perror | displays a character string corresponding of the current error to stderr (function) [edit]
##### Operations on files
remove | erases a file (function) [edit]
rename | renames a file (function) [edit]
tmpfile | creates and opens a temporary, auto-removing file (function) [edit]
tmpnam | returns a unique filename (function) [edit]

### [edit] Types

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

### [edit] Macros

Defined in header `<cstdio>`
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)
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_SET SEEK_CUR SEEK_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 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)

### [edit] See also

C documentation for File input/output

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