Specializations of the class templatestd::fpos identify absolute positions in a stream or in a file. Each object of typefpos holds the byte position in the stream (typically as a private member of typestd::streamoff) and the current shift state, a value of typeState (typicallystd::mbstate_t).

The following typedef names forstd::fpos<std::mbstate_t> are provided (although they are spelled differently in the standard, they denote the same type):

All specializations offpos meet theDefaultConstructible,CopyConstructible,CopyAssignable,Destructible, andEqualityComparable requirements.

IfState is trivially copy constructible,fpos has a trivial copy constructor. IfState is trivially copy assignable,fpos has a trivial copy assignment operator. IfState is trivially destructible,fpos has a trivial destructor.

[edit]Template parameter

[edit]Member functions

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 value-initializes the state object. This constructor must also accept the special valuestd::streamoff(-1): thestd::fpos constructed in this manner is returned by some stream operations to indicate errors.

• Explicit conversion from (possibly const)fpos tostd::streamoff. The result is the stored offset.

• operator== andoperator!= that compare two objects of type (possibly const)std::fpos and return abool prvalue.p!= q is equivalent to!(p== q).

• operator+ andoperator- such that, for an objectp of type (possibly const)fpos<State> and an objecto of type (possibly const)std::streamoff

• p+ o has typefpos<State> and stores an offset that is the result of addingo to the offset ofp.
• o+ p has a type convertible tofpos<State> and the result of the conversion is equal top+ o.
• p- o has typefpos<State> and stores an offset that is the result of subtractingo from the offset ofp.

• operator+= andoperator-= 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 anstd::streamoff, such that for two such objectsp andq,p== q+(p- q).

[edit]Notes

Some of theI/O streams member functions return and manipulate objects of member typedefpos_type. For streams, these member typedefs are provided by the template parameterTraits, which defaults tostd::char_traits, which define theirpos_types to be specializations ofstd::fpos. The behavior of the I/O streams library is implementation-defined whenTraits::pos_type is notstd::fpos<std::mbstate_t> (akastd::streampos,std::wstreampos, etc.).

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit]See also

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