fpos(3C++) - fpos(3C++)
Standard C++ Library Copyright 1998, Rogue Wave Software, Inc.
NAMEfpos
- Maintains position information fort he iostream classes.
SYNOPSIS
#include <rw/iotraits>
template<class stateT = mbstate_t>
class fposDESCRIPTION
The template class_fpos<stateT> is used by the iostream classes to
maintain position information. It maintains three kinds of information:
the absolute position, the conversion state and the validity of the
stored position. Streams instantiated on tiny characters use stream‐
pos_as their positioning type, whereas streams instantiated on wide
characters use wstreampos, but both are defined as fpos<mbstate_t>.
INTERFACE
template <class stateT = mbstate_t>
class fpos {
public:
typedef stateT state_type;
fpos(long off = 0);
fpos(state_type);
bool good();
operator long();
long offset() cont;
long offset(long);
state_type state(state_type);
state_type state () const;
long pos() const;
long pos(long);
};
TYPES
state_type
The type state_type holds the conversion state, and is compatible with the
function locale::codecvt(). By default it is defined as mbstate_t.
PUBLIC CONSTRUCTORS
fpos(long off =0);
Constructs an fpos object, initializing its position with off and its con‐
version state with the default stateT constructor. This function is not
described in the C++ standard.
fpos(state_type st);
Constructs an fpos object, initializing its conversion state with st, its
position with the start position, and its status to good.
PUBLIC MEMBER FUNCTIONS
state_type
state() const;
Returns the conversion state stored in the fpos object.
state_typestate(state_type st);
Stores st as the new conversion state in the fpos object and returns its
previous value.
bool good();
Returns the status of the fpos object. Offset(-1) indicates an invalid
value and returns false.
operator long();
Converts fpos object to absolute displacement. This operator is handy when
used with functions such as tellp() or tellg() to get absolute displace‐
ment.
longoffset() const;
Returns the signed displacement in the fpos object.
longoffset(long off);
Stores off as the new signed displacement in the fpos object and returns
its previous value.
longpos() const;
Returns the absolute position in the fpos object.
longoffset(long pos);
Stores pos as the new absolute position in the fpos object and returns its
previous value.
VALID OPERATIONS
In the following,
· P refers to type fpos<stateT>
· p and q refer to a value of type fpos<stateT>
· O refers to the offset type (streamoff, wstreamoff, long )
· o refers to a value of the offset type
· i refers to a value of type int
Valid operations:
P p( I ); Constructs from int
P p = i; Assigns from int
P( o ) Converts from offset
O( p ) Converts to offset
p == q Tests for equality
p != q Tests for inequality
q = p + o Adds offset
p += o Adds offset
q = p -o Subtracts offset
q -= o Subtracts offset
o = p - q Returns offset
SEE ALSO
iosfwd(3C++), char_traits(3C++)
Working Paper for Draft Proposed International Standard for Information
Systems--Programming Language C++, Section 27.4.
Amendment 1 to the C Standard.
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
Rogue Wave Software 02 Apr 1998 fpos(3C++)
