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{{cpp/title|ios_base}}
{{cpp/io/ios_base/navbar}}
{{ddcl|header=ios|
class ios_base;
}}

The class {{tt|ios_base}} is a multipurpose class that serves as the base class for all I/O stream classes. It maintains several kinds of data:

@1@ state information: stream status flags.
@2@ control information: flags that control formatting of both input and output sequences and the imbued locale.
@3@ private storage: indexed extensible data structure that allows both {{c/core|long}} and {{c/core|void*}} members, which may be implemented as two arbitrary-length arrays or a single array of two-element structs or another container.
@4@ callbacks: arbitrary number of user-defined functions to be called from {{ltf|cpp/io/ios_base/imbue}}, {{lc|std::basic_ios::copyfmt()}}, and {{ltf|cpp/io/ios_base/~ios_base}}.

Typical implementation holds member constants corresponding to all values of {{ltt|cpp/io/ios_base/fmtflags}}, {{ltt|cpp/io/ios_base/iostate}}, {{ltt|cpp/io/ios_base/openmode}}, and {{ltt|cpp/io/ios_base/seekdir}} shown below, member variables to maintain current precision, width, and formatting flags, the exception mask, the buffer error state, a resizeable container holding the callbacks, the currently imbued locale, the private storage, and a static integer variable for {{ltf|cpp/io/ios_base/xalloc}}.

===Member functions===
{{dsc begin}}
{{dsc inc|cpp/io/ios_base/dsc constructor}}
{{dsc inc|cpp/io/ios_base/dsc destructor}}
{{dsc inc|cpp/io/ios_base/dsc operator{{=}}}}

{{dsc h2|Formatting}}
{{dsc inc|cpp/io/ios_base/dsc flags}}
{{dsc inc|cpp/io/ios_base/dsc setf}}
{{dsc inc|cpp/io/ios_base/dsc unsetf}}
{{dsc inc|cpp/io/ios_base/dsc precision}}
{{dsc inc|cpp/io/ios_base/dsc width}}

{{dsc h2|Locales}}
{{dsc inc|cpp/io/ios_base/dsc imbue}}
{{dsc inc|cpp/io/ios_base/dsc getloc}}

{{dsc h2|Internal extensible array}}
{{dsc inc|cpp/io/ios_base/dsc xalloc}}
{{dsc inc|cpp/io/ios_base/dsc iword}}
{{dsc inc|cpp/io/ios_base/dsc pword}}

{{dsc h2|Miscellaneous}}
{{dsc inc|cpp/io/ios_base/dsc register_callback}}
{{dsc inc|cpp/io/ios_base/dsc sync_with_stdio}}

{{dsc h1|Member classes}}
{{dsc inc|cpp/io/ios_base/dsc failure}}
{{dsc inc|cpp/io/ios_base/dsc Init}}
{{dsc end}}

{{dsc begin}}
{{dsc h1|Member types and constants}}
{{dsc hitem|Type|Explanation}}
{{dsc inc|cpp/io/ios_base/dsc openmode}}
{{dsc inc|cpp/io/ios_base/dsc fmtflags}}
{{dsc inc|cpp/io/ios_base/dsc iostate}}
{{dsc inc|cpp/io/ios_base/dsc seekdir}}
{{dsc inc|cpp/io/ios_base/dsc event}}
{{dsc inc|cpp/io/ios_base/dsc event_callback}}
{{dsc end}}
{{rev begin}}
{{rev|until=c++17|
{{dsc begin}}
{{dsc h2|Deprecated member types}}
{{dsc hitem|Type|Explanation}}
{{dsc|{{tt|io_state}} {{mark deprecated}}|integer type that may be used like {{tt|iostate}}}}
{{dsc|{{tt|open_mode}} {{mark deprecated}}|integer type that may be used like {{tt|openmode}}}}
{{dsc|{{tt|seek_dir}} {{mark deprecated}}|integer type that may be used like {{tt|seekdir}}}}
{{dsc|{{tt|streamoff}} {{mark deprecated}}|unspecified type that may be used like {{tt|off_type}}, not necessarily {{lc|std::streamoff}}}}
{{dsc|{{tt|streampos}} {{mark deprecated}}|unspecified type that may be used like {{tt|pos_type}}, not necessarily {{lc|std::streampos}}}}
{{dsc end}}
}}
{{rev end}}

===Defect reports===
{{dr list begin}}
{{dr list item|wg=lwg|dr=1357|paper=N3110|std=C++98|before={{tt|std::ios_base}} defined {{c/core|operator~}}, {{c/core|operator&}}<br>and {{c/core|operator{{!}}}} for types {{tt|openmode}}, {{tt|fmtflags}} and<br>{{tt|iostate}}, violating the requirements of {{named req|BitmaskType}}<ref>A {{named req|BitmaskType}} needs to support bitwise opertaions on its own. The bitwise operation support should not be provided externally.</ref>|after=removed these definitions}}
{{dr list end}}
<references/>

===See also===
{{dsc begin}}
{{dsc inc|cpp/io/dsc basic_ios}}
{{dsc end}}

{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

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