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Difference between revisions of "cpp/io/basic ios"

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Microsoft Visual Studio stores just those three members.
 
Microsoft Visual Studio stores just those three members.
  
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LLVM libc++ stores 1 less member: it maintains the rdbuf pointer as a void* member of ios_base.
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LLVM libc++ stores 1 less member: it maintains the {{tt|rdbuf}} pointer as a {{c/core|void*}} member of {{tt|ios_base}}.
  
 
GNU libstdc++ stores 4 additional members: three cached facets and a flag to indicate that fill was initialized
 
GNU libstdc++ stores 4 additional members: three cached facets and a flag to indicate that fill was initialized
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Revision as of 08:48, 22 January 2023

 
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

Two specializations for common character types are also provided:

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

Contents

Member types

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

Public member functions

 constructs the object
(public member function) [edit]
[virtual]
 destructs the object
(virtual public member function) [edit]
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) [edit]
checks if end-of-file has been reached
(public member function) [edit]
checks if an error has occurred
(public member function) [edit]
checks if a non-recoverable error has occurred
(public member function) [edit]
checks if an error has occurred (synonym of fail())
(public member function) [edit]
checks if no error has occurred (synonym of !fail())
(public member function) [edit]
returns state flags
(public member function) [edit]
sets state flags
(public member function) [edit]
modifies state flags
(public member function) [edit]
Formatting
copies formatting information
(public member function) [edit]
manages the fill character
(public member function) [edit]
Miscellaneous
manages exception mask
(public member function) [edit]
sets the locale
(public member function) [edit]
manages associated stream buffer
(public member function) [edit]
manages tied stream
(public member function) [edit]
narrows characters
(public member function) [edit]
widens characters
(public member function) [edit]

Protected member functions

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

Inherited from std::ios_base

Member functions

Formatting
manages format flags
(public member function of std::ios_base) [edit]
sets specific format flag
(public member function of std::ios_base) [edit]
clears specific format flag
(public member function of std::ios_base) [edit]
manages decimal precision of floating point operations
(public member function of std::ios_base) [edit]
manages field width
(public member function of std::ios_base) [edit]
Locales
sets locale
(public member function of std::ios_base) [edit]
returns current locale
(public member function of std::ios_base) [edit]
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) [edit]
resizes the private storage if necessary and access to the long element at the given index
(public member function of std::ios_base) [edit]
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
registers event callback function
(public member function of std::ios_base) [edit]
[static]
 sets whether C++ and C I/O libraries are interoperable
(public static member function of std::ios_base) [edit]
Member classes
stream exception
(public member class of std::ios_base) [edit]
initializes standard stream objects
(public member class of std::ios_base) [edit]

Member types and constants

Type Explanation
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]
noreplace (C++23) open in exclusive mode[edit]

(typedef) [edit]
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. 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. 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 operations: see std::uppercase[edit]

(typedef) [edit]
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]
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]
specifies event type
(enum) [edit]
callback function type
(typedef) [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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