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# std::basic_ios

From cppreference.com
< cpp‎ | io

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.

Inheritance diagram

Two specializations for common character types are also provided:

Type | Definition
`ios` | basic_ios<char>
`wios` | basic_ios<wchar_t>

### [edit] Member types

Member type | Definition
`char_type` | CharT[edit]
`traits_type` | Traits[edit]
`int_type` | Traits::int_type[edit]
`pos_type` | Traits::pos_type[edit]
`off_type` | Traits::off_type[edit]

### [edit] Public member functions

(constructor) | constructs the object (public member function) [edit]
(destructor) [virtual] | destructs the object (virtual public member function) [edit]
operator= | the copy assignment operator is deleted (public member function)
##### State functions
good | checks if no error has occurred i.e. I/O operations are available (public member function) [edit]
eof | checks if end-of-file has been reached (public member function) [edit]
fail | checks if an error has occurred (public member function) [edit]
bad | checks if a non-recoverable error has occurred (public member function) [edit]
operator! | checks if an error has occurred (synonym of fail()) (public member function) [edit]
operator void*operator bool (until C++11)(since C++11) | checks if no error has occurred (synonym of !fail()) (public member function) [edit]
rdstate | returns state flags (public member function) [edit]
setstate | sets state flags (public member function) [edit]
clear | clears error and eof flags (public member function) [edit]
##### Formatting
copyfmt | copies formatting information (public member function) [edit]
fill | manages the fill character (public member function) [edit]
##### Miscellaneous
exceptions | manages exception mask (public member function) [edit]
imbue | sets the locale (public member function) [edit]
rdbuf | manages associated stream buffer (public member function) [edit]
tie | manages tied stream (public member function) [edit]
narrow | narrows characters (public member function) [edit]
widen | widens characters (public member function) [edit]

### [edit] Protected member functions

init | initializes a default-constructed std::basic_ios (protected member function) [edit]
move (C++11) | moves from another std::basic_ios except for `rdbuf` (protected member function) [edit]
swap (C++11) | swaps with another std::basic_ios except for `rdbuf` (protected member function) [edit]
set_rdbuf | replaces the `rdbuf` without clearing its error state (protected member function) [edit]

## Inherited from std::ios_base

### Member functions

##### Formatting
flags | manages format flags (public member function of `std::ios_base`) [edit]
setf | sets specific format flag (public member function of `std::ios_base`) [edit]
unsetf | clears specific format flag (public member function of `std::ios_base`) [edit]
precision | manages decimal precision of floating point operations (public member function of `std::ios_base`) [edit]
width | manages field width (public member function of `std::ios_base`) [edit]
##### Locales
imbue | sets locale (public member function of `std::ios_base`) [edit]
getloc | returns current locale (public member function of `std::ios_base`) [edit]
##### Internal extensible array
xalloc [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`) [edit]
iword | resizes the private storage if necessary and access to the long element at the given index (public member function of `std::ios_base`) [edit]
pword | resizes the private storage if necessary and access to the void* element at the given index (public member function of `std::ios_base`) [edit]
##### Miscellaneous
register_callback | registers event callback function (public member function of `std::ios_base`) [edit]
sync_with_stdio [static] | sets whether C++ and C IO libraries are interoperable (public static member function of `std::ios_base`) [edit]
##### Member classes
failure | stream exception (public member class of `std::ios_base`) [edit]
Init | initializes standard stream objects (public member class of `std::ios_base`) [edit]

### Member types and constants
Type | Explanation
openmode | stream open mode type The following constants are also defined:
Constant | Explanation[edit]
`app` | seek to the end of stream before each write[edit]
`binary` | open in binary mode[edit]
`in` | open for reading[edit]
`out` | open for writing[edit]
`trunc` | discard the contents of the stream when opening[edit]
`ate` | seek to the end of stream immediately after open[edit]
(typedef) [edit]
fmtflags | formatting flags type The following constants are also defined:
Constant | Explanation[edit]
`dec` | use decimal base for integer I/O: see std::dec[edit]
`oct` | use octal base for integer I/O: see std::oct[edit]
`hex` | use hexadecimal base for integer I/O: see std::hex[edit]
`basefield` | dec|oct|hex|0. Useful for masking operations[edit]
`left` | left adjustment (adds fill characters to the right): see std::left [edit]
`right` | right adjustment (adds fill characters to the left): see std::right [edit]
`internal` | internal adjustment (adds fill characters to the internal designated point): see std::internal [edit]
`adjustfield` | left|right|internal. Useful for masking operations [edit]
`scientific` | generate floating point types using scientific notation, or hex notation if combined with fixed: see std::scientific [edit]
`fixed` | generate floating point types using fixed notation, or hex notation if combined with scientific: see std::fixed [edit]
`floatfield` | scientific|fixed|(scientific|fixed)|0. Useful for masking operations [edit]
`boolalpha` | insert and extract bool type in alphanumeric format: see std::boolalpha [edit]
`showbase` | generate a prefix indicating the numeric base for integer output, require the currency indicator in monetary I/O: see std::showbase [edit]
`showpoint` | generate a decimal-point character unconditionally for floating-point number output: see std::showpoint [edit]
`showpos` | generate a + character for non-negative numeric output: see std::showpos [edit]
`skipws` | skip leading whitespace before certain input operations: see std::skipws [edit]
`unitbuf` | flush the output after each output operation: see std::unitbuf [edit]
`uppercase` | replace certain lowercase letters with their uppercase equivalents in certain output output operations: see std::uppercase [edit]
(typedef) [edit]
iostate | state of the stream type The following constants are also defined:
Constant | Explanation[edit]
`goodbit` | no error [edit]
`badbit` | irrecoverable stream error [edit]
`failbit` | input/output operation failed (formatting or extraction error) [edit]
`eofbit` | associated input sequence has reached end-of-file [edit]
(typedef) [edit]
seekdir | seeking direction type The following constants are also defined:
Constant | Explanation[edit]
`beg` | the beginning of a stream [edit]
`end` | the ending of a stream [edit]
`cur` | the current position of stream position indicator [edit]
(typedef) [edit]
event | specifies event type (enum) [edit]
event_callback | callback function type (typedef) [edit]

### [edit] 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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