Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.

NAME

 
fpos
 
 - Maintains position information fort he iostream classes.
 
 
 

SYNOPSIS

 
 
#include <rw/iotraits>
template<class stateT = mbstate_t>
class fpos
 
 
 

DESCRIPTION

 
 
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 streampos_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 conversion 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_type
state(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 displacement. 
 

 
 
long
offset() const;

 
 
Returns the signed displacement in the fpos object.
 

 
 
long
offset(long off);

 
 
Stores off as the new signed displacement in the fpos object and returns its previous value. 
 

 
 
long
pos() const;

 
 
Returns the absolute position in the fpos object.
 

 
 
long
offset(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  —  Last change: 02 Apr 1998