The header <ostream> defines a type and several function signatures that control output to a stream buffer along with a function template that inserts into stream rvalues.
namespace std {
template <class charT, class traits = char_traits<charT> >
class basic_ostream : virtual public basic_ios<charT,traits> {
public:
// types (inherited from basic_ios ([ios])):
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 traits traits_type;
// [ostream.cons] Constructor/destructor:
explicit basic_ostream(basic_streambuf<char_type,traits>* sb);
virtual ~basic_ostream();
// [ostream::sentry] Prefix/suffix:
class sentry;
// [ostream.formatted] Formatted output:
basic_ostream<charT,traits>& operator<<(
basic_ostream<charT,traits>& (*pf)(basic_ostream<charT,traits>&));
basic_ostream<charT,traits>& operator<<(
basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&));
basic_ostream<charT,traits>& operator<<(
ios_base& (*pf)(ios_base&));
basic_ostream<charT,traits>& operator<<(bool n);
basic_ostream<charT,traits>& operator<<(short n);
basic_ostream<charT,traits>& operator<<(unsigned short n);
basic_ostream<charT,traits>& operator<<(int n);
basic_ostream<charT,traits>& operator<<(unsigned int n);
basic_ostream<charT,traits>& operator<<(long n);
basic_ostream<charT,traits>& operator<<(unsigned long n);
basic_ostream<charT,traits>& operator<<(long long n);
basic_ostream<charT,traits>& operator<<(unsigned long long n);
basic_ostream<charT,traits>& operator<<(float f);
basic_ostream<charT,traits>& operator<<(double f);
basic_ostream<charT,traits>& operator<<(long double f);
basic_ostream<charT,traits>& operator<<(const void* p);
basic_ostream<charT,traits>& operator<<(
basic_streambuf<char_type,traits>* sb);
// [ostream.unformatted] Unformatted output:
basic_ostream<charT,traits>& put(char_type c);
basic_ostream<charT,traits>& write(const char_type* s, streamsize n);
basic_ostream<charT,traits>& flush();
// [ostream.seeks] seeks:
pos_type tellp();
basic_ostream<charT,traits>& seekp(pos_type);
basic_ostream<charT,traits>& seekp(off_type, ios_base::seekdir);
protected:
basic_ostream(const basic_ostream& rhs) = delete;
basic_ostream(basic_ostream&& rhs);
// [ostream.assign] Assign/swap
basic_ostream& operator=(const basic_ostream& rhs) = delete;
basic_ostream& operator=(basic_ostream&& rhs);
void swap(basic_ostream& rhs);
};
// [ostream.inserters.character] character inserters
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);
// signed and unsigned
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*);
// signed and unsigned
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*);
}
The class basic_ostream defines a number of member function signatures that assist in formatting and writing output to output sequences controlled by a stream buffer.
Two groups of member function signatures share common properties: the formatted output functions (or inserters) and the unformatted output functions. Both groups of output functions generate (or insert) output characters by actions equivalent to calling rdbuf()->sputc(int_type). They may use other public members of basic_ostream except that they shall not invoke any virtual members of rdbuf() except overflow(), xsputn(), and sync().
If one of these called functions throws an exception, then unless explicitly noted otherwise the output function sets badbit in error state. If badbit is on in exceptions(), the output function rethrows the exception without completing its actions, otherwise it does not throw anything and treat as an error.
explicit basic_ostream(basic_streambuf<charT,traits>* sb);
Effects: Constructs an object of class basic_ostream, assigning initial values to the base class by calling basic_ios<charT,traits>::init(sb) ([basic.ios.cons]).
Effects: Destroys an object of class basic_ostream.
Remarks: Does not perform any operations on rdbuf().
basic_ostream(basic_ostream&& rhs);
Effects: Move constructs from the rvalue rhs. This is accomplished by default constructing the base class and calling basic_ios<charT, traits>::move(rhs) to initialize the base class.
basic_ostream& operator=(basic_ostream&& rhs);
Effects: swap(rhs).
Returns: *this.
void swap(basic_ostream& rhs);
Effects: Calls basic_ios<charT, traits>::swap(rhs).
namespace std {
template <class charT,class traits = char_traits<charT> >
class basic_ostream<charT,traits>::sentry {
bool ok_; // exposition only
public:
explicit sentry(basic_ostream<charT,traits>& os);
~sentry();
explicit operator bool() const { return ok_; }
sentry(const sentry&) = delete;
sentry& operator=(const sentry&) = delete;
};
}
The class sentry defines a class that is responsible for doing exception safe prefix and suffix operations.
If os.good() is nonzero, prepares for formatted or unformatted output. If os.tie() is not a null pointer, calls os.tie()->flush().325
If, after any preparation is completed, os.good() is true, ok_ == true otherwise, ok_ == false. During preparation, the constructor may call setstate(failbit) (which may throw ios_base::failure ([iostate.flags]))326
If ((os.flags() & ios_base::unitbuf) && !uncaught_exception() && os.good()) is true, calls os.rdbuf()->pubsync(). If that function returns -1, sets badbit in os.rdstate() without propagating an exception.
explicit operator bool() const;
Effects: Returns ok_.
The call os.tie()->flush() does not necessarily occur if the function can determine that no synchronization is necessary.
The sentry constructor and destructor can also perform additional implementation-dependent operations.
Each seek member function begins execution by constructing an object of class sentry. It returns by destroying the sentry object.
Returns:
If
fail() != false,
returns
pos_type(-1)
to indicate failure.
Otherwise, returns
rdbuf()->pubseekoff(0, cur, out).
basic_ostream<charT,traits>& seekp(pos_type pos);
Effects: If fail() != true, executes rdbuf()->pubseekpos(pos, ios_base::out). In case of failure, the function calls setstate(failbit) (which may throw ios_base::failure).
Returns: *this.
basic_ostream<charT,traits>& seekp(off_type off, ios_base::seekdir dir);
Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base::out). In case of failure, the function calls setstate(failbit) (which may throw ios_base::failure).
Returns: *this.
Each formatted output function begins execution by constructing an object of class sentry. If this object returns true when converted to a value of type bool, the function endeavors to generate the requested output. If the generation fails, then the formatted output function does setstate(ios_base::failbit), which might throw an exception. If an exception is thrown during output, then ios::badbit is turned on327 in *this's error state. If (exceptions()&badbit) != 0 then the exception is rethrown. Whether or not an exception is thrown, the sentry object is destroyed before leaving the formatted output function. If no exception is thrown, the result of the formatted output function is *this.
The descriptions of the individual formatted output functions describe how they perform output and do not mention the sentry object.
If a formatted output function of a stream os determines padding, it does so as follows. Given a charT character sequence seq where charT is the character type of the stream, if the length of seq is less than os.width(), then enough copies of os.fill() are added to this sequence as necessary to pad to a width of os.width() characters. If (os.flags() & ios_base::adjustfield) == ios_base::left is true, the fill characters are placed after the character sequence; otherwise, they are placed before the character sequence.
without causing an ios::failure to be thrown.
operator<<(bool val);
operator<<(short val);
operator<<(unsigned short val);
operator<<(int val);
operator<<(unsigned int val);
operator<<(long val);
operator<<(unsigned long val);
operator<<(long long val);
operator<<(unsigned long long val);
operator<<(float val);
operator<<(double val);
operator<<(long double val);
operator<<(const void* val);
Effects: The classes num_get<> and num_put<> handle locale-dependent numeric formatting and parsing. These inserter functions use the imbued locale value to perform numeric formatting. When val is of type bool, long, unsigned long, long long, unsigned long long, double, long double, or const void*, the formatting conversion occurs as if it performed the following code fragment:
bool failed = use_facet<
num_put<charT,ostreambuf_iterator<charT,traits> >
>(getloc()).put(*this, *this, fill(), val).failed();
When val is of type short the formatting conversion occurs as if it performed the following code fragment:
ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield;
bool failed = use_facet<
num_put<charT,ostreambuf_iterator<charT,traits> >
>(getloc()).put(*this, *this, fill(),
baseflags == ios_base::oct || baseflags == ios_base::hex
? static_cast<long>(static_cast<unsigned short>(val))
: static_cast<long>(val)).failed();
When val is of type int the formatting conversion occurs as if it performed the following code fragment:
ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield;
bool failed = use_facet<
num_put<charT,ostreambuf_iterator<charT,traits> >
>(getloc()).put(*this, *this, fill(),
baseflags == ios_base::oct || baseflags == ios_base::hex
? static_cast<long>(static_cast<unsigned int>(val))
: static_cast<long>(val)).failed();
When val is of type unsigned short or unsigned int the formatting conversion occurs as if it performed the following code fragment:
bool failed = use_facet<
num_put<charT,ostreambuf_iterator<charT,traits> >
>(getloc()).put(*this, *this, fill(),
static_cast<unsigned long>(val)).failed();
When val is of type float the formatting conversion occurs as if it performed the following code fragment:
bool failed = use_facet<
num_put<charT,ostreambuf_iterator<charT,traits> >
>(getloc()).put(*this, *this, fill(),
static_cast<double>(val)).failed();
The first argument provides an object of the ostreambuf_iterator<> class which is an iterator for class basic_ostream<>. It bypasses ostreams and uses streambufs directly. Class locale relies on these types as its interface to iostreams, since for flexibility it has been abstracted away from direct dependence on ostream. The second parameter is a reference to the base subobject of type ios_base. It provides formatting specifications such as field width, and a locale from which to obtain other facets. If failed is true then does setstate(badbit), which may throw an exception, and returns.
Returns: *this.
basic_ostream<charT,traits>& operator<<
(basic_ostream<charT,traits>& (*pf)(basic_ostream<charT,traits>&));
Effects: None. Does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
basic_ostream<charT,traits>& operator<<
(basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&));
Effects: Calls pf(*this). This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
basic_ostream<charT,traits>& operator<<
(ios_base& (*pf)(ios_base&));
Effects: Calls pf(*this). This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
Returns: *this.
basic_ostream<charT,traits>& operator<<
(basic_streambuf<charT,traits>* sb);
Effects: Behaves as an unformatted output function (as described in [ostream.unformatted], paragraph 1). After the sentry object is constructed, if sb is null calls setstate(badbit) (which may throw ios_base::failure).
Gets characters from sb and inserts them in *this. Characters are read from sb and inserted until any of the following occurs:
end-of-file occurs on the input sequence;
inserting in the output sequence fails (in which case the character to be inserted is not extracted);
an exception occurs while getting a character from sb.
If the function inserts no characters, it calls setstate(failbit) (which may throw ios_base::failure ([iostate.flags])). If an exception was thrown while extracting a character, the function sets failbit in error state, and if failbit is on in exceptions() the caught exception is rethrown.
Returns: *this.
See, for example, the function signature endl(basic_ostream&) ([ostream.manip]).
See, for example, the function signature dec(ios_base&) ([basefield.manip]).
template<class charT, class traits>
basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
charT c);
template<class charT, class traits>
basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
char c);
// specialization
template<class traits>
basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
char c);
// signed and unsigned
template<class traits>
basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
signed char c);
template<class traits>
basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
unsigned char c);
Effects: Behaves as a formatted output function ( [ostream.formatted.reqmts]) of out. Constructs a character sequence seq. If c has type char and the character type of the stream is not char, then seq consists of out.widen(c); otherwise seq consists of c. Determines padding for seq as described in [ostream.formatted.reqmts]. Inserts seq into out. Calls os.width(0).
Returns: out.
template<class charT, class traits>
basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
const charT* s);
template<class charT, class traits>
basic_ostream<charT,traits>& operator<<(basic_ostream<charT,traits>& out,
const char* s);
template<class traits>
basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
const char* s);
template<class traits>
basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
const signed char* s);
template<class traits>
basic_ostream<char,traits>& operator<<(basic_ostream<char,traits>& out,
const unsigned char* s);
Requires: s shall not be a null pointer.
Effects: Behaves like a formatted inserter (as described in [ostream.formatted.reqmts]) of out. Creates a character sequence seq of n characters starting at s, each widened using out.widen() ([basic.ios.members]), where n is the number that would be computed as if by:
traits::length(s) for the overload where the first argument is of type basic_ostream<charT, traits>& and the second is of type const charT*, and also for the overload where the first argument is of type basic_ostream<char, traits>& and the second is of type const char*,
std::char_traits<char>::length(s) for the overload where the first argument is of type basic_ostream<charT, traits>& and the second is of type const char*,
traits::length(reinterpret_cast<const char*>(s)) for the other two overloads.
Determines padding for seq as described in [ostream.formatted.reqmts]. Inserts seq into out. Calls width(0).
Returns: out.
Each unformatted output function begins execution by constructing an object of class sentry. If this object returns true, while converting to a value of type bool, the function endeavors to generate the requested output. If an exception is thrown during output, then ios::badbit is turned on330 in *this's error state. If (exceptions() & badbit) != 0 then the exception is rethrown. In any case, the unformatted output function ends by destroying the sentry object, then, if no exception was thrown, returning the value specified for the unformatted output function.
Effects: Behaves as an unformatted output function (as described in [ostream.unformatted], paragraph 1). After constructing a sentry object, inserts the character c, if possible.331
Otherwise, calls setstate(badbit) (which may throw ios_base::failure ([iostate.flags])).
Returns: *this.
basic_ostream& write(const char_type* s, streamsize n);
Effects: Behaves as an unformatted output function (as described in [ostream.unformatted], paragraph 1). After constructing a sentry object, obtains characters to insert from successive locations of an array whose first element is designated by s.332 Characters are inserted until either of the following occurs:
n characters are inserted;
inserting in the output sequence fails (in which case the function calls setstate(badbit), which may throw ios_base::failure ([iostate.flags])).
Returns: *this.
Effects: Behaves as an unformatted output function (as described in [ostream.formatted.reqmts], paragraph 1). If rdbuf() is not a null pointer, constructs a sentry object. If this object returns true when converted to a value of type bool the function calls rdbuf()->pubsync(). If that function returns -1 calls setstate(badbit) (which may throw ios_base::failure ([iostate.flags])). Otherwise, if the sentry object returns false, does nothing.
Returns: *this.
without causing an ios::failure to be thrown.
Note that this function is not overloaded on types signed char and unsigned char.
Note that this function is not overloaded on types signed char and unsigned char.
namespace std {
template <class charT, class traits>
basic_ostream<charT,traits>& endl(basic_ostream<charT,traits>& os);
}
Effects: Calls os.put(os.widen('\n')), then os.flush().
Returns: os.
namespace std {
template <class charT, class traits>
basic_ostream<charT,traits>& ends(basic_ostream<charT,traits>& os);
}
Effects: Inserts a null character into the output sequence: calls os.put(charT()).
Returns: os.
namespace std {
template <class charT, class traits>
basic_ostream<charT,traits>& flush(basic_ostream<charT,traits>& os);
}
Effects: Calls os.flush().
Returns: os.
template <class charT, class traits, class T>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>&& os, const T& x);
Effects: os << x
Returns: os