std::fpos
Defined in header
<ios>
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template< class State >
class fpos; |
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Specializations of the class template std::fpos identify absolute positions in a stream or in a file. Each object of type fpos
holds the byte position in the stream (typically as a private member of type std::streamoff) and the current shift state, a value of type State
(typically std::mbstate_t).
The following specializations of std::fpos are provided:
Type | Definition |
streampos
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std::fpos<std::char_traits<char>::state_type> |
wstreampos
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std::fpos<std::char_traits<wchar_t>::state_type> |
In addition, std::u16streampos and std::u32streampos are provided as implementation-defined types that satisfy the requirements of |
(since C++11) |
[edit] Member functions
gets/sets the value of the shift state (public member function) |
In addition, the following member functions and operators must be provided, although it's unspecified if they are members or non-member.
- A constructor that accepts an argument of type int.
- A constructor that accepts an argument of type std::streamoff. This constructor must also accept the special value std::streamoff(-1): the
std::fpos
constructed in this manner is returned by some stream operations to indicate errors.
- A conversion operator that converts
fpos
to std::streamoff with the value equal to the offset fromstd::fpos(0)
.
- operator== that compares two objects of type
std::fpos
and returns a value of type convertible to bool
- operator!= that compares two objects of type
std::fpos
and returns a value of type convertible to bool
- operator+ and operator+= which can add std::streamoff to
std::fpos
- operator- and operator-= which can subtract std::streamoff from an
std::fpos
- operator- which can subtract two objects of type
std::fpos
producing an std::streamoff
[edit] Notes
std::streampos
and std::wstreampos
are required to be the same type because std::char_traits<char>::state_type and std::char_traits<wchar_t>::state_type are required to both be std::mbstate_t. C++98 had a self-contradictory statement that they may be different if the implementation supports no shift encoding in narrow-oriented iostreams but supports one or more shift encodings in wide-oriented streams, but that was corrected in C++03.
Some of the I/O streams member functions return and manipulate objects of member typedef pos_type
. For streams, these member typedefs are provided by the template parameter Traits
, which defaults to std::char_traits, which define their pos_type
s to be specializations of std::fpos
. The behavior of the I/O streams library is implementation-defined when Traits::pos_type is not std::fpos<std::mbstate_t> (aka std::streampos or std::wstreampos).
[edit] See also
represents relative file/stream position (offset from fpos), sufficient to represent any file size (typedef) |
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returns the output position indicator (public member function of std::basic_ostream )
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sets the output position indicator (public member function of std::basic_ostream )
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gets the file position indicator (function) |