std::basic_ios

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< cpp‎ | io
 
C++
 
Input/output library
 
std::basic_ios
 
Defined in header <ios>
template<

    class CharT,
    class Traits = std::char_traits<CharT>
> class basic_ios

    : public std::ios_base

The class std::basic_ios provides facilities for interfacing with objects that have std::basic_streambuf interface. Several std::basic_ios objects can refer to one actual std::basic_streambuf object.

cpp/io/ios basestd-basic ios-inheritance.svg

Inheritance diagram

Several typedefs for common character types are provided:

Defined in header <ios>
Type Definition
std::ios std::basic_ios<char>
std::wios std::basic_ios<wchar_t>

Member types

Member type Definition
char_type CharT
traits_type Traits; the program is ill-formed if Traits::char_type is not CharT.
int_type Traits::int_type
pos_type Traits::pos_type
off_type Traits::off_type

Public member functions

 constructs the object
(public member function)
[virtual]
 destructs the object
(virtual public member function)
operator=
 the copy assignment operator is deleted
(public member function)
State functions
checks if no error has occurred i.e. I/O operations are available
(public member function)
checks if end-of-file has been reached
(public member function)
checks if an error has occurred
(public member function)
checks if a non-recoverable error has occurred
(public member function)
checks if an error has occurred (synonym of fail())
(public member function)
checks if no error has occurred (synonym of !fail())
(public member function)
returns state flags
(public member function)
sets state flags
(public member function)
modifies state flags
(public member function)
Formatting
copies formatting information
(public member function)
manages the fill character
(public member function)
Miscellaneous
manages exception mask
(public member function)
sets the locale
(public member function)
manages associated stream buffer
(public member function)
manages tied stream
(public member function)
narrows characters
(public member function)
widens characters
(public member function)

Protected member functions

 initializes a default-constructed std::basic_ios
(protected member function)
(C++11)
 moves from another std::basic_ios except for rdbuf
(protected member function)
(C++11)
 swaps with another std::basic_ios except for rdbuf
(protected member function)
replaces the rdbuf without clearing its error state
(protected member function)

Inherited from std::ios_base

Member functions

Formatting
manages format flags
(public member function of std::ios_base)
sets specific format flag
(public member function of std::ios_base)
clears specific format flag
(public member function of std::ios_base)
manages decimal precision of floating point operations
(public member function of std::ios_base)
manages field width
(public member function of std::ios_base)
Locales
sets locale
(public member function of std::ios_base)
returns current locale
(public member function of std::ios_base)
Internal extensible array
[static]
 returns a program-wide unique integer that is safe to use as index to pword() and iword()
(public static member function of std::ios_base)
resizes the private storage if necessary and access to the long element at the given index
(public member function of std::ios_base)
resizes the private storage if necessary and access to the void* element at the given index
(public member function of std::ios_base)
Miscellaneous
registers event callback function
(public member function of std::ios_base)
[static]
 sets whether C++ and C I/O libraries are interoperable
(public static member function of std::ios_base)
Member classes
stream exception
(public member class of std::ios_base)
initializes standard stream objects
(public member class of std::ios_base)

Member types and constants

Type Explanation
stream open mode type

The following constants are also defined:

Constant Explanation
app seek to the end of stream before each write
binary open in binary mode
in open for reading
out open for writing
trunc discard the contents of the stream when opening
ate seek to the end of stream immediately after open
noreplace (C++23) open in exclusive mode

(typedef)
formatting flags type

The following constants are also defined:

Constant Explanation
dec use decimal base for integer I/O: see std::dec
oct use octal base for integer I/O: see std::oct
hex use hexadecimal base for integer I/O: see std::hex
basefield dec | oct | hex. Useful for masking operations
left left adjustment (adds fill characters to the right): see std::left
right right adjustment (adds fill characters to the left): see std::right
internal internal adjustment (adds fill characters to the internal designated point): see std::internal
adjustfield left | right | internal. Useful for masking operations
scientific generate floating point types using scientific notation, or hex notation if combined with fixed: see std::scientific
fixed generate floating point types using fixed notation, or hex notation if combined with scientific: see std::fixed
floatfield scientific | fixed. Useful for masking operations
boolalpha insert and extract bool type in alphanumeric format: see std::boolalpha
showbase generate a prefix indicating the numeric base for integer output, require the currency indicator in monetary I/O: see std::showbase
showpoint generate a decimal-point character unconditionally for floating-point number output: see std::showpoint
showpos generate a + character for non-negative numeric output: see std::showpos
skipws skip leading whitespace before certain input operations: see std::skipws
unitbuf flush the output after each output operation: see std::unitbuf
uppercase replace certain lowercase letters with their uppercase
equivalents in certain output operations: see std::uppercase

(typedef)
state of the stream type

The following constants are also defined:

Constant Explanation
goodbit no error
badbit irrecoverable stream error
failbit input/output operation failed (formatting or extraction error)
eofbit associated input sequence has reached end-of-file

(typedef)
seeking direction type

The following constants are also defined:

Constant Explanation
beg the beginning of a stream
end the ending of a stream
cur the current position of stream position indicator

(typedef)
specifies event type
(enum)
callback function type
(typedef)

Notes

Straightforward implementation of std::basic_ios stores only the following members (which all depend on the template parameters and thus cannot be part of std::ios_base):

  • the fill character (see fill())
  • the tied stream pointer (see tie())
  • the associated stream buffer pointer (see rdbuf()).

Actual implementations vary:

Microsoft Visual Studio stores just those three members.

LLVM libc++ stores 1 less member: it maintains the rdbuf pointer as a void* member of ios_base.

GNU libstdc++ stores 4 additional members: three cached facets and a flag to indicate that fill was initialized.

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