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C-style file input/output

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Revision as of 13:08, 12 February 2014 by Cubbi (Talk | contribs)

 
 
 
 

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).

Contents

Functions

File access
opens a file
(function) [edit]
open an existing stream with a different name
(function) [edit]
closes a file
(function) [edit]
synchronizes an output stream with the actual file
(function) [edit]
switches a file stream between wide character I/O and narrow character I/O
(function) [edit]
sets the buffer for a file stream
(function) [edit]
sets the buffer and its size for a file stream
(function) [edit]
Direct input/output
reads from a file
(function) [edit]
writes to a file
(function) [edit]
Unformatted input/output
Narrow character
gets a character from a file stream
(function) [edit]
gets a character string from a file stream
(function) [edit]
writes a character to a file stream
(function) [edit]
writes a character string to a file stream
(function) [edit]
reads a character from stdin
(function) [edit]
(until C++14)
reads a character string from stdin
(function) [edit]
writes a character to stdout
(function) [edit]
writes a character string to stdout
(function) [edit]
puts a character back into a file stream
(function) [edit]
Wide character
gets a wide character from a file stream
(function) [edit]
gets a wide string from a file stream
(function) [edit]
writes a wide character to a file stream
(function) [edit]
writes a wide string to a file stream
(function) [edit]
reads a wide character from stdin
(function) [edit]
writes a wide character to stdout
(function) [edit]
puts a wide character back into a file stream
(function) [edit]
Formatted input/output
Narrow/multibyte character
reads formatted input from stdin, a file stream or a buffer
(function) [edit]
(C++11)(C++11)(C++11)
reads formatted input from stdin, a file stream or a buffer
using variable argument list
(function) [edit]
prints formatted output to stdout, a file stream or a buffer
(function) [edit]
prints formatted output to stdout, a file stream or a buffer
using variable argument list
(function) [edit]
Wide character
reads formatted wide character input from stdin, a file stream or a buffer
(function) [edit]
(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]
prints formatted wide character output to stdout, a file stream or a buffer
(function) [edit]
prints formatted wide character output to stdout, a file stream
or a buffer using variable argument list
(function) [edit]
File positioning
returns the current file position indicator
(function) [edit]
gets the file position indicator
(function) [edit]
moves the file position indicator to a specific location in a file
(function) [edit]
moves the file position indicator to a specific location in a file
(function) [edit]
moves the file position indicator to the beginning in a file
(function) [edit]
Error handling
clears errors
(function) [edit]
checks for the end-of-file
(function) [edit]
checks for a file error
(function) [edit]
displays a character string corresponding of the current error to stderr
(function) [edit]
Operations on files
erases a file
(function) [edit]
renames a file
(function) [edit]
creates and opens a temporary, auto-removing file
(function) [edit]
returns a unique filename
(function) [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

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)