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std::fpos(3) C++ Standard Libary std::fpos(3) NAME std::fpos - std::fpos Synopsis Defined in header <ios> template< class State > class fpos; 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 posi- tion in the stream (typically as a private member of type std::streamoff) and the cur- rent shift state, a value of type State (typically std::mbstate_t). The following typedef names for std::fpos<std::mbstate_t> are pro- vided (although they are spelled differently in the standard, they denote the same type): Defined in header <iosfwd> Type Definition streampos std::fpos<std::char_traits<char>::state_type> wstreampos std::fpos<std::char_traits<wchar_t>::state_type> u8streampos (C++20) std::fpos<std::char_traits<char8_t>::state_type> u16streampos (C++11) std::fpos<std::char_traits<char16_t>::state_type> u32streampos (C++11) std::fpos<std::char_traits<char32_t>::state_type> All specializations of fpos meet the DefaultConstructible, CopyCon- structible, CopyAssignable, Destructible, and EqualityComparable requirements. If State is trivially copy constructible, fpos has a trivial copy constructor. If State is trivially copy assignable, fpos has a trivial copy assign- ment operator. If State is trivially destructible, fpos has a trivial destructor. Template parameter State - the type representing the shift state Type requirements - State must meet the requirements of Destructible, CopyAssignable, CopyConstructible and DefaultConstructible. Member functions state gets/sets the value of the shift state (public member function) In addition, member and non-member functions are provided to support the following operations: * A default constructor that stores an offset of zero and value- initializes the state object. * A non-explicit constructor that accepts an argument of type (possibly const) std::streamoff, which stores that offset and and value-initial- izes the state object. 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. * Explicit conversion from (possibly const) fpos to std::streamoff. The result is the stored offset. * operator== and operator!= that compare two objects of type (pos- sibly const) std::fpos and returns a value of type convertible to bool. p != q is equivalent to !(p == q). * operator+ and operator- such that, for an object p of type (pos- sibly const) fpos<State> and an object o of type (possibly const) std::streamoff * p + o has type fpos<State> and stores an offset that is the result of adding o to the offset of p * o + p has a type convertible to fpos<State> and the re- sult of the conversion is equal to p + o * p - o has type fpos<State> and stores an offset that is the result of subtracting o from the offset of p * operator+= and operator-= which can accept a (possibly const) std::streamoff and adds/subtracts it from the stored offset, respectively. * operator- which can subtract two objects of type (possibly const) std::fpos producing an std::streamoff, such that for two such objects p and q, p == q + (p - q) Notes Some of the I/O streams member functions return and manipulate ob- jects 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_types 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, std::wstreampos, etc.). Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior streampos and wstreampos were LWG 57 C++98 contradictionally allowed to be different clarified to be same whiled required to be same P0759R1 C++98 specification was unclear and incomplete cleaned up P1148R0 C++11 unclear what and in which header the made clear definition u16streampos and u32streampos are See also represents relative file/stream position (offset from fpos), sufficient to streamoff represent any file size (typedef) tellp returns the output position indicator (public member function of std::basic_os- tream<CharT,Traits>) seekp sets the output position indicator (public member function of std::basic_os- tream<CharT,Traits>) fgetpos gets the file position indicator (function) http://cppreference.com 2022.07.31 std::fpos(3)
NAME | Synopsis | Type requirements | Member functions | Notes | See also
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