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Standard C++ Library
Copyright 1998, Rogue Wave Software, Inc.
NAME
basic_ostream
- Assists in formatting and writing output to sequences
controlled by a stream buffer.
SYNOPSIS
#include <ostream>
template<class charT, class traits = char_traits<charT> >
class basic_ostream
: virtual public basic_ios<charT, traits>
DESCRIPTION
The class basic_ostream defines member functions that assist
in formatting and writing output to sequences controlled by
a stream buffer.
Two groups of member functions share common properties: the
formatted output functions (or insertors) and the unformat-
ted output functions. Both groups of functions insert char-
acters by calling basic_streambuf member functions. They
both begin by constructing an object of class
basic_ostream::sentry and, if this object is in good state
after construction, the function tries to perform the
requested output. The sentry object performs exception-safe
initialization, such as controlling the status of the stream
or locking it in a multithread environment.
Some formatted output functions generate the requested out-
put by converting a value from some scalar to text form and
inserting the converted text in the output sequence. The
conversion behavior is directly depend on the locale object
being imbued in the stream.
INTERFACE
template<class charT, class traits = char_traits<charT> >
class basic_ostream
:virtual public basic_ios<charT, traits> {
public:
typedef traits traits_type;
typedef charT char_type;
typedef typename traits::int_type int_type;
typedef typename traits::pos_type pos_type;
typedef typename traits::off_type off_type;
typedef basic_ostream<charT, traits> ostream_type;
typedef basic_ios<charT, traits> ios_type;
explicit basic_ostream(basic_streambuf<charT, traits>
*sb);
virtual ~basic_ostream();
class sentry {
public:
explicit sentry(basic_ostream<charT,traits>&);
~sentry();
operator bool ();
};
ostream_type& operator<<(ostream_type&
(*pf)(ostream_type&));
ostream_type& operator<<(ios_base& (*pf)(ios_base&));
ostream_type& operator<<(ios_type& (*pf)(ios_type&));
ostream_type& operator<<(bool n);
ostream_type& operator<<(short n);
ostream_type& operator<<(unsigned short n);
ostream_type& operator<<(int n);
ostream_type& operator<<(unsigned int n);
ostream_type& operator<<(long n);
ostream_type& operator<<(unsigned long n);
ostream_type& operator<<(float f);
ostream_type& operator<<(double f);
ostream_type& operator<<(long double f);
ostream_type& operator<<(const void *p);
ostream_type&
operator<<(basic_streambuf<char_type,traits> &sb);
ostream_type&
operator<<(basic_streambuf<char_type,traits> *sb);
ostream_type& put(char_type c);
ostream_type& write(const char_type *s, streamsize n);
ostream_type& flush();
pos_type tellp();
ostream_type& seekp(pos_type );
ostream_type& seekp(off_type , ios_base::seekdir );
protected:
basic_ostream();
};
//global character inserter functions
template <class charT, class traits>
basic_ostream<charT,traits>&
operator<<(basic_ostream<charT,traits>&, charT);
template <class charT, class traits>
basic_ostream<charT,traits>&
operator<<(basic_ostream<charT,traits>&, char);
template <class traits>
basic_ostream<char,traits>&
operator<<(basic_ostream<char,traits>&, char);
template <class traits>
basic_ostream<char,traits>&
operator<<(basic_ostream<char,traits>&, signed char);
template <class traits>
basic_ostream<char,traits>&
operator<<(basic_ostream<char,traits>&, unsigned char);
template <class charT, class traits>
basic_ostream<charT,traits>&
operator<<(basic_ostream<charT,traits>&, const charT*);
template <class charT, class traits>
basic_ostream<charT,traits>&
operator<<(basic_ostream<charT,traits>&, const char*);
template <class traits>
basic_ostream<char,traits>&
operator<<(basic_ostream<char,traits>&, const char*);
template <class traits>
basic_ostream<char,traits>&
operator<<(basic_ostream<char,traits>&, const signed char*);
template <class traits>
basic_ostream<char,traits>&
operator<<(basic_ostream<char,traits>&,
const unsigned char*);
template<class charT, class traits>
basic_ostream<charT, traits>&
endl(basic_ostream<charT, traits>& os);
template<class charT, class traits>
basic_ostream<charT, traits>&
ends(basic_ostream<charT, traits>& os);
template<class charT, class traits>
basic_ostream<charT, traits>&
flush(basic_ostream<charT, traits>& os);
TYPES
char_type
The type char_type is a synonym for the template parame-
ter charT.
int_type
The type int_type is a synonym of type traits::in_type.
ios_type
The type ios_type is a synonym for basic_ios<charT,
traits>.
off_type
The type off_type is a synonym of type traits::off_type.
ostream
The type ostream is an instantiation of class
basic_ostream on type char:
typedef basic_ostream<char> ostream;
ostream_type
The type ostream_type is a synonym for
basic_ostream<charT, traits>.
pos_type
The type pos_type is a synonym of type traits::pos_type.
traits_type
The type traits_type is a synonym for the template param-
eter traits.
wostream
The type wostream is an instantiation of class
basic_ostream on type wchar_t:
typedef basic_ostream<wchar_t> wostream;
CONSTRUCTORS
explicit basic_ostream(basic_streambuf<charT, traits>* sb);
Constructs an object of class basic_ostream, assigning
initial values to the base class by calling
basic_ios<charT,traits>::init(sb).
DESTRUCTORS
virtual ~basic_ostream();
Destroys an object of class basic_ostream.
SENTRY CLASSES
explicit sentry(basic_ostream<charT,traits>&);
Prepares for formatted or unformatted output. If the
basic_ios member function tie() is not a null pointer,
the function synchronizes the output sequence with any
associated stream. If after any preparation is completed,
the basic_ios member function good() is true, the sentry
conversion function operator bool() returns true. Other-
wise it returns false. In a multithread environment the
sentry object constructor is responsible for locking the
stream and the stream buffer associated with the stream.
~sentry();
Destroys an object of class sentry. If the ios_base
member function flags() & unitbuf == true, then flushes
the buffer. In a multithread environment the sentry
object destructor is responsible for unlocking the stream
and the stream buffer associated with the stream.
operator bool();
If after any preparation is completed, the ios_base
member function good() is true, the sentry conversion
function operator bool() returns true, else it returns
false.
INSERTORS
ostream_type&
operator<<(ostream_type& (*pf) (ostream_type&));
Calls pf(*this), then returns *this. See, for example,
the function signature endl(basic_ostream&).
ostream_type&
operator<<(ios_type& (*pf) (ios_type&));
Calls pf(*this), then returns *this.
ostream_type&
operator<<(ios_base& (*pf) (ios_base&));
Calls pf(*this), then returns *this. See, for example,
the function signature dec(ios_base&).
ostream_type&
operator<<(bool n);
Converts the boolean value n and outputs it into the
basic_ostream object's buffer. If the ios_base member
function flag() & ios_base::boolalpha is false it tries
to write an integer value, which must be 0 or 1. If the
boolalpha flag is true, it writes characters according to
the locale function numpunct<>::truename() or
numpunct<>::falsename().
ostream_type&
operator<<(short n);
Converts the signed short integer n, and outputs it into
the stream buffer, then returns *this.
ostream_type&
operator<<(unsigned short n);
Converts the unsigned short integer n, and outputs it
into the stream buffer, then returns *this.
ostream_type&
operator<<(int n);
Converts the signed integer n, and outputs it into the
stream buffer, then returns *this.
ostream_type&
operator<<(unsigned int n);
Converts the unsigned integer n, and outputs it into the
stream buffer, then returns *this.
ostream_type&
operator<<(long n);
Converts the signed long integer n, and outputs it into
the stream buffer, then returns *this.
ostream_type&
operator<<(unsigned long n);
Converts the unsigned long integer n, and outputs it into
the stream buffer, then returns *this.
ostream_type&
operator<<(float f);
Converts the float f and outputs it into the stream
buffer, then returns *this.
ostream_type&
operator<<(double f);
Converts the double f and outputs it into the stream
buffer, then returns *this.
ostream_type&
operator<<(long double f);
Converts the long double f and outputs it into the stream
buffer, then returns *this.
ostream_type&
operator<<(void *p);
Converts the pointer p, and outputs it into the stream
buffer, then returns *this.
ostream_type&
operator<<(basic_streambuf<charT,traits> *sb);
If sb is null calls the basic_ios member function
setstate(badbit). Otherwise gets characters from sb and
inserts them into the stream buffer until any of the fol-
lowing occurs:
- An end-of-file on the input sequence.
- A failure when inserting in the output sequence
- An exception while getting a character from sb
If the function inserts no characters or if it stopped
because an exception was thrown while extracting a char-
acter, it calls the basic_ios member function
setstate(failbit). If an exception was thrown while
extracting a character, it is rethrown.
ostream_type&
operator<<(basic_streambuf<charT,traits>& sb);
Gets characters from sb and inserts them into the stream
buffer until any of the following occurs:
- An end-of-file on the input sequence.
- A failure when inserting in the output sequence
- An exception while getting a character from sb
If the function inserts no characters or if it stopped
because an exception was thrown while extracting a char-
acter, it calls the basic_ios member function
setstate(failbit). If an exception was thrown while
extracting a character it is rethrown.
UNFORMATTED FUNCTIONS
ostream_type&
flush();
If rdbuf() is not a null pointer, calls rdbuf()-
>pubsync() and returns *this. If that function returns
-1, calls setstate(badbit).
ostream_type&
put(char_type c);
Inserts the character c. If the operation fails, calls
the basic_ios member function setstate(badbit).
ostream_type&
seekp(pos_type pos);
If the basic_ios member function fail() returns false,
executes rdbuf()->pubseekpos(pos), which positions the
current pointer of the output sequence at the position
designated by pos.
ostream_type&
seekp(off_type off, ios_base::seekdir dir);
If the basic_ios member function fail() returns false,
executes rdbuf()->pubseekpos(off,dir), which positions
the current pointer of the output sequence at the posi-
tion designated by off and dir.
pos_type
tellp();
If the basic_ios member function fail() returns true,
tellp() returns pos_type(off_type(-1)) to indicate
failure. Otherwise it returns the current position of the
output sequence by calling rdbuf()-> pubseekoff(0,cur,
out).
ostream_type&
write(const char_type* s, streamsize n);
Obtains characters to insert from successive locations of
an array whose first element is designated by s. Charac-
ters are inserted until either of the following occurs:
- n characters are inserted
- Inserting in the output sequence fails
In the second case the function calls the basic_ios
member function setstate(badbit). The function returns
*this.
NON-MEMBER FUNCTIONS
template<class charT, class traits>
basic_ostream<charT, traits>&
endl(basic_ostream<charT, traits>& os);
Outputs a newline character and flushes the buffer, then
returns os.
template<class charT, class traits>
basic_ostream<charT, traits>&
ends(basic_ostream<charT, traits>& os);
Inserts a null character into the output sequence, then
returns os.
template<class charT, class traits>
basic_ostream<charT, traits>&
flush(basic_ostream<charT, traits>& os);
Flushes the buffer, then returns os.
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, charT c);
Outputs the character c of type charT into the
basic_ostream object's buffer. Both the stream and the
stream buffer are instantiated on type charT. Padding is
not ignored.
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, char c);
Outputs the character c of type char into the
basic_ostream object's buffer. Both the stream and the
stream buffer are instantiated on type charT. Conversion
from characters of type char to characters of type charT
is performed by the basic_ios member function widen. Pad-
ding is not ignored.
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os, char c);
Outputs the character c of type char into the
basic_ostream object's buffer. Both the stream and the
stream buffer are instantiated on type char. Padding is
not ignored.
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os,
const charT* s);
Outputs the null-terminated-byte-string s of type charT*
into the basic_ostream object's buffer. Both the stream
and the stream buffer are instantiated on type charT.
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os,
const char* s);
Outputs the null-terminated-byte-string s of type char*
into the basic_ostream object's buffer. Both the stream
and the stream buffer are instantiated on type charT.
Conversion from characters of type char to characters of
type charT is performed by the basic_ios member function
widen.
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os, const char* s);
Outputs the null-terminated-byte-string s of type char*
into the basic_ostream object's buffer. Both the stream
and the stream buffer are instantiated on type char.
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os,
unsigned char c);
Returns os << (char)c.
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os, signed char c);
Returns os << (char)c.
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os,
unsigned char* c);
Returns os << (char*)c.
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os,
signed char* c);
Returns os << (char*)c.
FORMATTING
The formatting is done through member functions or manipula-
tors.
Manipulators Member Functions
showpos setf(ios_base::showpos)
noshowpos unsetf(ios_base::showpos)
showbase setf(ios_base::showbase)
noshowbase unsetf(ios_base::showbase)
uppercase setf(ios_base::uppercase)
nouppercase unsetf(ios_base::uppercase)
showpoint setf(ios_base::showpoint)
noshowpoint unsetf(ios_base::showpoint)
boolalpha setf(ios_base::boolalpha)
noboolalpha unsetf(ios_base::boolalpha)
unitbuf setf(ios_base::unitbuf)
nounitbuf unsetf(ios_base::unitbuf)
internal setf(ios_base::internal,
ios_base::adjustfield)
left setf(ios_base::left,
ios_base::adjustfield)
right setf(ios_base::right,
ios_base::adjustfield)
dec setf(ios_base::dec,
ios_base::basefield)
hex setf(ios_base::hex,
ios_base::basefield)
oct setf(ios_base::oct,
ios_base::basefield)
fixed setf(ios_base::fixed,
ios_base::floatfield)
scientific setf(ios_base::scientific,
ios_base::floatfield)
resetiosflags
(ios_base::fmtflags flag) setf(0,flag)
setiosflags
(ios_base::fmtflags flag) setf(flag)
setbase(int base) see above
setfill(char_type c) fill(c)
setprecision(int n) precision(n)
setw(int n) width(n)
DESCRIPTION
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 uncondition-
ally 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 positions)
of certain generated output
right Adds fill characters on the left (initial positions)
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 nota-
tion
scientific Generates floating-point output in scientific
notation
resetiosflags
(ios_base::fmtflags flag) Resets the fmtflags field flag
setiosflags
(ios_base::fmtflags flag) Sets up the flag flag
setbase(int base) Converts integer input or generates
integer output in base base. The parame-
ter base can be 8, 10 or 16.
setfill(char_type c) Sets the character used to pad (fill)
an output conversion to the specified
field width
setprecision(int n) Sets the precision (number of digits
after the decimal point) to generate
on certain output conversions
setw(int n) Sets the field with (number of characters) to
generate on certain output conversions
EXAMPLE
//
// stdlib/examples/manual/ostream1.cpp
//
#include<iostream>
#include<ostream>
#include<sstream>
#include<iomanip>
void main ( )
{
using namespace std;
float f= 3.14159;
int i= 22;
const char* s= "Randy is the king of stdlib";
// create a read/write stringbuf object on tiny char
// and attach it to an istringstream object
istringstream in( ios_base::in | ios_base::out );
// tie the ostream object to the istringstream object
ostream out(in.rdbuf());
out << "test beginning !" << endl;
// output i in hexadecimal
out << hex << i <<endl;
// set the field width to 10
// set the padding character to '@'
// and output i in octal
out << setw(10) << oct << setfill('@') << i << endl;
// set the precision to 2 digits after the separator
// output f
out << setprecision(3) << f << endl;
// output the 17 first characters of s
out.write(s,17);
// output a newline character
out.put('\n');
// output s
out << s << endl;
// output the all buffer to standard output
cout << in.rdbuf();
}
//
// stdlib/examples/manual/ostream2.cpp
//
#include<iostream>
#include<ostream>
#include<sstream>
void main ( )
{
using namespace std;
float f= 3.14159;
const wchar_t* s= L"Kenavo !";
// create a read/write stringbuf object on wide char
// and attach it to an wistringstream object
wistringstream in( ios_base::in | ios_base::out );
// tie the wostream object to the wistringstream object
wostream out(in.rdbuf());
out << L"test beginning !" << endl;
// output f in scientific format
out << scientific << f <<endl;
// store the current put-pointer position
wostream::pos_type pos = out.tellp();
// output s
out << s << endl;
// output the all buffer to standard output
wcout << in.rdbuf() << endl;
// position the get-pointer
in.seekg(pos);
// output s
wcout << in.rdbuf() << endl;
}
SEE ALSO
char_traits(3C++), ios_base(3C++), basic_ios(3C++),
basic_streambuf(3C++), basic_iostream(3C++)
Working Paper for Draft Proposed International Standard for
Information Systems--Programming Language C++, Section
27.6.2.1
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
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