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Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.
NAME
ios_base
- Defines member types and maintains data for classes that
inherit from it.
SYNOPSIS
#include <ios>
class ios_base;
DESCRIPTION
The class_ios_base defines several member types:
o A class failure derived from exception.
o A class Init.
o Three bitmask types: fmtflags, iostate, and openmode.
o Two enumerated types: seekdir and event.
It maintains several kinds of data:
o Control information that influences how to interpret
(format) input sequences and how to generate (format)
output sequences.
o Locale object used within the stream classes.
o Additional information that is stored by the program
for its private use.
INTERFACE
class ios_base {
public:
class failure : public exception {
public:
explicit failure(const string& msg);
virtual ~failure() throw();
virtual const char* what() const throw();
};
typedef int fmtflags;
enum fmt_flags {
boolalpha = 0x0001,
dec = 0x0002,
fixed = 0x0004,
hex = 0x0008,
internal = 0x0010,
left = 0x0020,
oct = 0x0040,
right = 0x0080,
scientific = 0x0100,
showbase = 0x0200,
showpoint = 0x0400,
showpos = 0x0800,
skipws = 0x1000,
unitbuf = 0x2000,
uppercase = 0x4000,
adjustfield = left | right | internal,
basefield = dec | oct | hex,
floatfield = scientific | fixed
};
typedef int iostate;
enum io_state {
goodbit = 0x00,
badbit = 0x01,
eofbit = 0x02,
failbit = 0x04
};
typedef int openmode;
enum open_mode {
app = 0x01,
binary = 0x02,
in = 0x04,
out = 0x08,
trunc = 0x10,
ate = 0x20
};
typedef int seekdir;
enum seek_dir {
beg = 0x0,
cur = 0x1,
end = 0x2
};
class Init;
fmtflags flags() const;
fmtflags flags(fmtflags fmtfl);
fmtflags setf(fmtflags fmtfl);
fmtflags setf(fmtflags fmtfl, fmtflags mask);
void unsetf(fmtflags mask);
streamsize precision() const;
streamsize precision(streamsize prec);
streamsize width() const;
streamsize width(streamsize wide);
locale imbue(const locale& loc);
locale getloc() const
static int xalloc();
long& iword(int index);
void*& pword(int index);
ios_base& copyfmt(const ios_base& rhs);
enum event {
erase_event = 0x0001,
imbue_event = 0x0002,
copyfmt_event = 0x004
};
typedef void (*event_callback) (event, ios_base&,
int index);
void register_callback(event_callback fn, int index);
bool synch_with_stdio(bool sync = true);
bool is_synch();
protected:
ios_base();
virtual ~ios_base();
private:
union ios_user_union {
long lword;
void* pword;
};
union ios_user_union *userwords_;
};
ios_base& boolalpha(ios_base&);
ios_base& noboolalpha(ios_base&);
ios_base& showbase(ios_base&);
ios_base& noshowbase(ios_base&);
ios_base& showpoint(ios_base&);
ios_base& noshowpoint(ios_base&);
ios_base& showpos(ios_base&);
ios_base& noshowpos(ios_base&);
ios_base& skipws(ios_base&);
ios_base& noskipws(ios_base&);
ios_base& uppercase(ios_base&);
ios_base& nouppercase(ios_base&);
ios_base& internal(ios_base&);
ios_base& left(ios_base&);
ios_base& right(ios_base&);
ios_base& dec(ios_base&);
ios_base& hex(ios_base&);
ios_base& oct(ios_base&);
ios_base& fixed(ios_base&);
ios_base& scientific(ios_base&);
ios_base& unitbuf(ios_base&);
ios_base& nounitbuf(ios_base&);
TYPES
fmtflags
The type fmtflags is a bitmask type. Setting its elements
has the following effects:
showpos Generates a + sign in non-negative generated
numeric output.
showbase Generates a prefix indicating the numeric base
of generated integer output
uppercase Replaces certain lowercase letters with their
uppercase equivalents in generated output
showpoint Generates a decimal-point character uncondi-
tionally in generated floating-point output
boolalpha Inserts and extracts bool type in alphabetic
format
unitbuf Flushes output after each output operation
internal Adds fill characters at a designated internal
point in certain generated output. If no such
point is designated, it's identical to right.
left Adds fill characters on the right (final posi-
tions) of certain generated output
right Adds fill characters on the left (initial posi-
tions) of certain generated output
dec Converts integer input or generates integer output
in decimal base
hex Converts integer input or generates integer output
in hexadecimal base
oct Converts integer input or generates integer output
in octal base
fixed Generates floating-point output in fixed-point
notation
scientific Generates floating-point output in scien-
tific notation
skipws Skips leading white space before certain input
operation.
iostate
The type iostate is a bitmask type. Setting its elements
has the following effects:
badbit Indicates a loss of integrity in an input or
output sequence.
eofbit Indicates that an input operation reached the
end of an input sequence.
failbit Indicates that an input operation failed to
read the expected characters, or that an output
operation failed to generate the desired char-
acters.
openmode
The type openmode is a bitmask type. Setting its elements
has the following effects:
app Seeks to the end before writing.
ate Opens and seeks to the end immediately after open-
ing.
binary Performs input and output in binary mode.
in Opens for input.
out Opens for output.
trunc Truncates an existing stream when opening.
seekdir
The type seekdir is a bitmask type. Setting its elements
has the following effects:
beg Requests a seek relative to the beginning of the
stream.
cur Requests a seek relative to the current position
within the sequence.
end Requests a seek relative to the current end of the
sequence.
event_callback
The type event_callback is the type of the callback func-
tion used as a parameter in the function
register_callback. These functions allow you to use the
iword, pword mechanism in an exception-safe environment.
PUBLIC CONSTRUCTORS
ios_base();
The ios_base members have an indeterminate value after
construction.
PUBLIC DESTRUCTORS
virtual
~ios_base();
Destroys an object of class ios_base. Calls each
registered callback pair (fn, index) as
(*fn)(erase_event,*this, index) at such a time that any
ios_base member function called from within fn has well-
defined results.
PUBLIC MEMBER FUNCTIONS
ios_base&
copyfmt(const ios_base& rhs);
Assigns to the member objects of *this the corresponding
member objects of rhs. The contents of the union pointed
to by pword and iword are copied, not the pointers them-
selves. Before copying any part of rhs, calls each
registered callback pair (fn,index) as
(*fn)(erase_even,*this, index). After all parts have been
replaced, calls each callback pair that was copied from
rhs as (*fn)(copy_event,*this,index).
fmtflags
flags() const;
Returns the format control information for both input and
output.
fmtflags
flags(fmtflags fmtfl);
Saves the format control information, then sets it to
fmtfl and returns the previously saved value.
locale
getloc() const;
Returns the imbued locale, which is used to perform
locale-dependent input and output operations. The default
locale, locale::locale(), is used if no other locale
object has been imbued in the stream by a call to the
imbue function.
locale
imbue(const locale& loc);
Saves the value returned by getloc(), then assigns loc to
a private variable and calls each registered callback
pair (fn, index) as (*fn)(imbue_event,*this, index). It
then returns the previously saved value.
bool
is_sync();
Returns true if the C++ standard streams and the standard
C streams are synchronized. Otherwise returns false. This
function is not part of the C++ standard.
long&
iword(int idx);
Returns userwords_[idx].iword. If userwords_ is a null
pointer, allocates a union of long and void* of unspeci-
fied size and stores a pointer to its first element in
userwords_. The function then extends the union pointed
to by userwords_ to include the element userwords_[idx].
Each newly allocated element of the union is initialized
to zero. The reference returned may become invalid after
another call to the object's iword or pword member with a
different index, after a call to its copyfmt member, or
when the object is destroyed.
streamsize
precision() const;
Returns the precision (number of digits after the decimal
point) to generate on certain output conversions.
streamsize
precision(streamsize prec);
Saves the precision, then sets it to prec and returns the
previously saved value.
void*&
pword(int idx);
Returns userword_[idx].pword. If userwords_ is a null
pointer, allocates a union of long and void* of unspeci-
fied size and stores a pointer to its first element in
userwords_. The function then extends the union pointed
to by userwords_ to include the element userwords_[idx].
Each newly allocated element of the array is initialized
to zero. The reference returned may become invalid after
another call to the object's pword or iword member with a
different index, after a call to its copyfmt member, or
when the object is destroyed.
void
register_callback(event_callback fn, int index);
Registers the pair (fn, index) such that during calls to
imbue(), copyfmt(), or ~ios_base(), the function fn is
called with argument index. Functions registered are
called when an event occurs, in opposite order of regis-
tration. Functions registered while a callback function
is active are not called until the next event. Identical
pairs are not merged; a function registered twice is
called twice per event.
fmtflags
setf(fmtflags fmtfl);
Saves the format control information, then sets it to
fmtfl and returns the previously saved value.
fmtflags
setf(fmtflags fmtfl, fmtflags mask);
Saves the format control information, then clears mask in
flags(), sets fmtfl & mask in flags() and returns the
previously saved value.
bool
sync_with_stdio(bool sync = true);
When called with a false argument, allows the C++ stan-
dard streams to operate independently of the standard C
streams, which greatly improves performance. When called
with a true argument, restores the default synchroniza-
tion. The return value of the function is the status of
the synchronization at the time of the call.
void
unsetf(fmtflags mask);
Clears mask in flags().
streamsize
width() const;
Returns the field width (number of characters) to gen-
erate on certain output conversions.
streamsize
width(streamsize wide);
Saves the field width, then sets it to wide and returns
the previously saved value.
static int
xalloc();
Returns the next static index that can be used with pword
and iword. This is useful if you want to share data
between several stream objects.
CLASS FAILURE
The class failure defines the base class for the types of
all objects thrown as exceptions by functions in the ios-
treams library. It reports errors detected during stream
buffer operations.
explicit failure(const string& msg);
Constructs an object of class failure, initializing the
base class with exception(msg).
const char*
what() const;
Returns the message msg with which the exception was
created.
CLASS INIT
The class Init describes an object whose construction
ensures the construction of the eight objects declared in
<iostream>, which associate file stream buffers with the
standard C streams.
NON-MEMBER FUNCTIONS
ios_base&
boolalpha(ios_base& str);
Calls str.setf(ios_base::boolalpha) and returns str.
ios_base&
dec(ios_base& str);
Calls str.setf(ios_base::dec, ios_base::basefield) and
returns str.
ios_base&
fixed(ios_base& str);
Calls str.setf(ios_base::fixed, ios_base::floatfield) and
returns str.
ios_base&
hex(ios_base& str);
Calls str.setf(ios_base::hex, ios_base::basefield) and
returns str.
ios_base&
internal(ios_base& str);
Calls str.setf(ios_base::internal, ios_base::adjustfield)
and returns str.
ios_base&
left(ios_base& str);
Calls str.setf(ios_base::left, ios_base::adjustfield) and
returns str.
ios_base&
noboolalpha(ios_base& str);
Calls str.unsetf(ios_base::boolalpha) and returns str.
ios_base&
noshowbase(ios_base& str);
Calls str.unsetf(ios_base::showbase) and returns str.
ios_base&
noshowpoint(ios_base& str);
Calls str.unsetf(ios_base::showpoint) and returns str.
ios_base&
noshowpos(ios_base& str);
Calls str.unsetf(ios_base::showpos) and returns str.
ios_base&
noskipws(ios_base& str);
Calls str.unsetf(ios_base::skipws) and returns str.
ios_base&
nounitbuf(ios_base& str);
Calls str.unsetf(ios_base::unitbuf) and returns str.
ios_base&
nouppercase(ios_base& str);
Calls str.unsetf(ios_base::uppercase) and returns str.
ios_base&
oct(ios_base& str);
Calls str.setf(ios_base::oct, ios_base::basefield) and
returns str.
ios_base&
right(ios_base& str);
Calls str.setf(ios_base::right, ios_base::adjustfield)
and returns str.
ios_base&
scientific(ios_base& str);
Calls str.setf(ios_base::scientific,
ios_base::floatfield) and returns str.
ios_base&
showbase(ios_base& str);
Calls str.setf(ios_base::showbase) and returns str.
ios_base&
showpoint(ios_base& str);
Calls str.setf(ios_base::showpoint) and returns str.
ios_base&
showpos(ios_base& str);
Calls str.setf(ios_base::showpos) and returns str.
ios_base&
skipws(ios_base& str);
Calls str.setf(ios_base::skipws) and returns str.
ios_base&
unitbuf(ios_base& str);
Calls str.setf(ios_base::unitbuf) and returns str.
ios_base&
uppercase(ios_base& str);
Calls str.setf(ios_base::uppercase) and returns str.
SEE ALSO
basic_ios(3C++), basic_istream(3C++), basic_ostream(3C++),
char_traits(3C++)
Working Paper for Draft Proposed International Standard for
Information Systems--Programming Language C++, Section
27.4.2
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
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