View source for cpp/io

{{title|Input/output library}}
{{cpp/io/sidebar}}

C++ includes two input/output libraries: a modern, stream-based I/O library and the standard set of C-style I/O functions.

===Stream-based I/O===

The stream-based input/output library is organized around abstract input/output devices. These abstract devices allow the same code to handle input/output to files, memory streams, or custom adaptor devices that perform arbitrary operations (e.g. compression) on the fly.

Most of the classes are templated, so they can be adapted to any basic character type. Separate typedefs are provided for the most common basic character types ({{c|char}} and {{c|wchar_t}}).  The classes are organized into the following hierarchy:

{{inheritance diagram|image=std-io-complete-inheritance.svg|map=
rect 215 4 318 36 [[cpp/io/ios_base]]
rect 206 69 327 107 [[cpp/io/basic_ios]]
rect 292 139 413 177 [[cpp/io/basic_istream]]
rect 120 139 241 177 [[cpp/io/basic_ostream]]
rect 395 280 515 318 [[cpp/io/basic_ifstream]]
rect 383 350 527 388 [[cpp/io/basic_istringstream]]
rect 206 209 327 247 [[cpp/io/basic_iostream]]
rect 17 280 138 318 [[cpp/io/basic_ofstream]]
rect 4 350 152 388 [[cpp/io/basic_ostringstream]]
rect 189 280 310 318 [[cpp/io/basic_fstream]]
rect 179 350 320 388 [[cpp/io/basic_stringstream]]
}}

{{dcl list begin}}
{{dcl list h2 | Abstraction}}
{{dcl list class | cpp/io/ios_base | manages formatting flags and input/output exceptions}}
{{dcl list tclass | cpp/io/basic_ios | manages an arbitrary stream buffer}}
{{dcl list tclass | cpp/io/basic_streambuf | abstracts a raw device}}
{{dcl list tclass | cpp/io/basic_istream | wraps a given abstract device ({{c|std::basic_streambuf}})<br/> and provides high-level input interface}}
{{dcl list tclass | cpp/io/basic_ostream | wraps a given abstract device ({{c|std::basic_streambuf}})<br/> and provides high-level output interface}}
{{dcl list tclass | cpp/io/basic_iostream | wraps a given abstract device ({{c|std::basic_streambuf}})<br/> and provides high-level input/output interface}}
{{dcl list h2 | File I/0 implementation}}
{{dcl list tclass | cpp/io/basic_filebuf | implements raw file device}}
{{dcl list tclass | cpp/io/basic_ifstream | implements high-level file stream input operations}}
{{dcl list tclass | cpp/io/basic_ofstream | implements high-level file stream output operations}}
{{dcl list tclass | cpp/io/basic_fstream | implements high-level file stream input/output operations}}
{{dcl list h2 | String I/0 implementation}}
{{dcl list tclass | cpp/io/basic_stringbuf | implements raw string device}}
{{dcl list tclass | cpp/io/basic_istringstream | implements high-level string stream input operations}}
{{dcl list tclass | cpp/io/basic_ostringstream | implements high-level string stream output operations}}
{{dcl list tclass | cpp/io/basic_stringstream | implements high-level string stream input/output operations}}
{{dcl list h2 | Array I/O implementations}}
{{dcl list class | cpp/io/strstreambuf | notes={{mark deprecated}} | implements raw character array device}}
{{dcl list class | cpp/io/istrstream | notes={{mark deprecated}} | implements character array input operations}}
{{dcl list class | cpp/io/ostrstream | notes={{mark deprecated}} | implements character array output operations}}
{{dcl list class | cpp/io/strstream | notes={{mark deprecated}} | implements character array input/output operations}}
{{dcl list end}}

====Typedefs====

The following typedefs for common character types are provided:

<source lang="cpp">
typedef basic_ios<char>                ios;
typedef basic_ios<wchar_t>            wios;

typedef basic_streambuf<char>     streambuf;
typedef basic_streambuf<wchar_t> wstreambuf;
typedef basic_filebuf<char>         filebuf;
typedef basic_filebuf<wchar_t>     wfilebuf;
typedef basic_stringbuf<char>     stringbuf;
typedef basic_stringbuf<wchar_t> wstringbuf;

typedef basic_istream<char>         istream;
typedef basic_istream<wchar_t>     wistream;
typedef basic_ostream<char>         ostream;
typedef basic_ostream<wchar_t>     wostream;
typedef basic_iostream<char>       iostream;
typedef basic_iostream<wchar_t>   wiostream;

typedef basic_ifstream<char>       ifstream;
typedef basic_ifstream<wchar_t>   wifstream;
typedef basic_ofstream<char>       ofstream;
typedef basic_ofstream<wchar_t>   wofstream;
typedef basic_fstream<char>         fstream;
typedef basic_fstream<wchar_t>     wfstream;

typedef basic_istringstream<char>     istringstream;
typedef basic_istringstream<wchar_t> wistringstream;
typedef basic_ostringstream<char>     ostringstream;
typedef basic_ostringstream<wchar_t> wostringstream;
typedef basic_stringstream<char>       stringstream;
typedef basic_stringstream<wchar_t>   wstringstream;
</source>

Predefined standard stream objects:
<source lang="cpp">
extern  istream  cin;   //standard input (stdin)
extern wistream wcin;
extern  ostream  cout;  //standard output (stdout)
extern wostream wcout;
extern  ostream  cerr;  //standard error (stderr)
extern wostream wcerr;
extern  ostream  clog;  //standard log (stdlog)
extern wostream wclog;
</source>

====[[cpp/io/manip|I/O Manipulators]]====

The stream-based I/O library uses [[cpp/io/manip| I/O manipulators]] (e.g. {{c|std::boolalpha}}, {{c|std::hex}}, etc.) to control how streams behave.

====Types====

The following auxiliary type are defined:
{{dcl list begin}}
{{dcl list header | ios }}
{{dcl list typedef | cpp/io/streamoff | represents relative file/stream position (offset from fpos), sufficient to represent any file size }}
{{dcl list typedef | cpp/io/streamsize | represents the number of characters transferred in an I/O operation or the size of an I/O buffer}}
{{dcl list tclass  | cpp/io/fpos | represents absolute position in a stream or a file}}
{{dcl list end}}

Four specializations of {{c|std::fpos}} are provided: 
{{dcl list begin}}
{{dcl list header | ios}}
{{dcl list hitem | Type | Definition}}
{{dcl list item | {{tt|streampos}} | {{c|std::fpos<std::char_traits<char>::state_type>}}}}
{{dcl list item | {{tt|u16streampos}} | {{c|std::fpos<std::char_traits<char16_t>::state_type>}}}}
{{dcl list item | {{tt|u32streampos}} | {{c|std::fpos<std::char_traits<char32_t>::state_type>}}}}
{{dcl list item | {{tt|wstreampos}} | {{c|std::fpos<std::char_traits<wchar_t>::state_type>}}}}
{{dcl list end}}

====Error category interface====
{{dcl list begin}}
{{dcl list header | ios }}
{{dcl list template | cpp/io/dcl list io_errc}}
{{dcl list template | cpp/io/dcl list iostream_category}}
<!-- TODO: these three specializations go inside the io_errc page 
{{dcl list ptfun | cpp/io/is_error_code_enum  | title=is_error_code_enum{{dcl small|(std::io_errc)}}| notes={{mark c++11}} | extends the type trait {{c|std::is_error_code_enum}} to identify iostream error codes}}
{{dcl list fun | cpp/io/make_error_code | title=make_error_code{{dcl small|(std::io_errc)}} | notes={{mark c++11}} | constructs an iostream error code}}
{{dcl list fun | cpp/io/make_error_condition  | title=make_error_condition{{dcl small|(std::io_errc)}} | notes={{mark c++11}} | constructs an iostream error_condition}}
-->
{{dcl list end}}

===[[cpp/io/c | C-style IO]]===

C++ also includes the [[cpp/io/c | input/output functions defined by C]], such as {{c|std::fopen}}, {{c|std::getc}}, etc.

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