basic_ostream

Library:  Input/output

basic_ostream  basic_ios  ios_base

• Local Index
• Summary
• Synopsis
• Description
• Interface
• Member Types
• Nonmember Types
• Constructor
• Destructor
• Class sentry
• Formatted Output Functions: Inserters
• Unformatted Output Functions
• Nonmember Functions
• Formatting
• Example
• See Also
• Standards Conformance

Members

basic_ostream() bool() char_type flush()

int_type off_type operator<<() pos_type

put() seekp() sentry() tellp()

traits_type write() ~basic_ostream() ~sentry()

Non-Members

endl() ends()

flush() operator<<()

ostream wostream

Class that assists in formatting and writing output to sequences controlled by a stream buffer

#include <ostream> 

namespace std {
  template<class charT, class traits = char_traits<charT> >
  class basic_ostream;
}

The class basic_ostream assists in formatting and writing output to sequences of characters controlled by a stream buffer. Two groups of functions share common properties, the formatted functions and the unformatted functions.

Both groups of functions insert output characters to basic_streambuf. 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 output 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.

namespace std {
  template <class charT, class traits = char_traits<charT> >
  class basic_ostream : virtual public basic_ios<charT,traits>
  {
   public:
    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;

    explicit 
    basic_ostream(basic_streambuf<char_type,traits>* sb);
    virtual ~basic_ostream();

    class sentry;

    basic_ostream& operator<<
      (basic_ostream& (*pf)(basic_ostream&));
    basic_ostream& operator<<
      (basic_ios<charT,traits>& (*pf)(basic_ios<charT,traits>&));
    basic_ostream& operator<<
      (ios_base& (*pf)(ios_base&));

    basic_ostream& operator<<(bool n);
    basic_ostream& operator<<(short n);
    basic_ostream& operator<<(unsigned short n);
    basic_ostream& operator<<(int n);
    basic_ostream& operator<<(unsigned int n);
    basic_ostream& operator<<(long n);
    basic_ostream& operator<<(unsigned long n);
    basic_ostream& operator<<(float f);
    basic_ostream& operator<<(double f);
    basic_ostream& operator<<(long double f);

    basic_ostream& operator<<(const void* p);
    basic_ostream& operator<<
      (basic_streambuf<char_type,traits>* sb);

    basic_ostream& put(char_type c);
    basic_ostream& write(const char_type* s, streamsize n);

    basic_ostream& flush();

    pos_type tellp();
    basic_ostream& seekp(pos_type);
    basic_ostream& seekp(off_type, ios_base::seekdir);
  };

  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*);
  }
}

char_type

The type char_type is a synonym for the template parameter charT.

int_type

The type int_type is a synonym of type traits::in_type.

off_type

The type off_type is a synonym of type traits::off_type.

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 parameter traits.

ostream

The type ostream is a specialization of class basic_ostream on type char:

typedef basic_ostream<char> ostream;

wostream

The type wostream is a specialization of class basic_ostream on type wchar_t:

typedef basic_ostream<wchar_t> wostream;

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);

virtual ~basic_ostream();

Destroys an object of class basic_ostream.

Interface

namespace std {  
  template <class charT,class traits = char_traits<charT> > 
  class basic_ostream<charT,traits>::sentry 
  { 
    public: 
    explicit sentry(basic_ostream<charT,traits>& os); 
    ~sentry(); 
    operator bool() const; 
    
    private: 
    sentry(const sentry&); // undefined 
    sentry& operator=(const sentry&); // undefined 
  }; 
}

Constructor

explicit sentry(basic_ostream<charT,traits>& os);

Prepares for formatted or unformatted output. If os.tie() is not a null pointer, the function synchronizes the output sequence with any associated stream. If after any preparation is completed, the os.good() is true, the sentry conversion function operator bool() returns true. Otherwise, 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.

Destructor

~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

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.

Formatted output functions start by constructing an object of class sentry. If this object returns true when converted to a value of type bool, the function attempts to produce the requested output. If the generation fails, the function calls setstate(ios::failbit), which might throw an exception. If an exception is thrown during output, ios::badbit is set in the stream object's error state without causing an ios::failure to be thrown.

If (exceptions()&badbit) != 0, the exception is rethrown. The sentry object is destroyed before the function exits. If no exception is thrown, the result of the formatted output function is *this.

basic_ostream& 
operator<<(basic_ostream& (*pf)(basic_ostream&));

Calls pf(*this), then returns *this. See, for example, the function signature endl(basic_ostream&).

basic_ostream& 
operator<<(basic_ios<char_type, traits_type>&
             (*pf)(basic_ios<char_type, traits_type>&));

Calls pf(*this), then returns *this.

basic_ostream& 
operator<<(ios_base& (*pf) (ios_base&));

Calls pf(*this), then returns *this. For example, see the function signature dec(ios_base&).

basic_ostream&  
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().

basic_ostream& 
operator<<(short n); 

Converts the signed short integer n, outputs it into the stream buffer, and returns *this.

basic_ostream& 
operator<<(unsigned short n); 

Converts the unsigned short integer n, outputs it into the stream buffer, and returns *this.

basic_ostream& 
operator<<(int n); 

Converts the signed integer n, outputs it into the stream buffer, and returns *this.

basic_ostream& 
operator<<(unsigned int n); 

Converts the unsigned integer n, outputs it into the stream buffer, and returns *this.

basic_ostream& 
operator<<(long n); 

Converts the signed long integer n, outputs it into the stream buffer, and returns *this.

basic_ostream& 
operator<<(unsigned long n); 

Converts the unsigned long integer n, outputs it into the stream buffer, and returns *this.

basic_ostream& 
operator<<(float f); 

Converts the float f, outputs it into the stream buffer, and returns *this.

basic_ostream& 
operator<<(double f); 

Converts the double f, outputs it into the stream buffer, and returns *this.

basic_ostream& 
operator<<(long double f); 

Converts the long double f, outputs it into the stream buffer, and returns *this.

basic_ostream& 
operator<<( const void *p); 

Converts the pointer p, outputs it into the stream buffer, and returns *this.

basic_ostream& 
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 following occurs:

• an end-of-file on the input sequence

• a failure when inserting into the output sequence

• an exception while getting a character from sb

If the function inserts no characters, or if it stops because an exception is thrown while extracting a character, it calls the basic_ios member function setstate(failbit). If an exception is thrown while extracting a character, it is rethrown.

basic_ostream& 
flush();

If rdbuf() is not a null pointer, calls rdbuf()->pubsync() and returns *this. If that function returns -1, calls setstate(badbit).

basic_ostream& 
put(char_type c); 

Inserts the character c. If the operation fails, calls the basic_ios member function setstate(badbit).

basic_ostream& 
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. If positioning fails, calls the basic_ios member function setstate(failbit).

basic_ostream& 
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 position designated by off and dir. If positioning fails, calls the basic_ios member function setstate(failbit).

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).

basic_ostream& 
write(const char_type* s, streamsize n); 

Obtains characters to insert from successive locations of an array whose first element is designated by s. Characters are inserted until either of the following occurs:

• n characters are inserted

• inserting into the output sequence fails

In the second case, the function calls the basic_ios member function setstate(badbit). The function returns *this.

template<class charT, class traits>
basic_ostream<charT, traits>&
endl(basic_ostream<charT, traits>& os); 

Outputs a newline character by calling os.put(os.widen ('\n')), flushes the buffer, and returns os.

template<class charT, class traits>
basic_ostream<charT, traits>&
ends(basic_ostream<charT, traits>& os); 

Inserts a null character, charT(), 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);
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, char c);
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os, char c);
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os, signed char c);
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os, unsigned char c);

Outputs the character c and any required padding into the basic_ostream object's buffer. If the type of c is char and it doesn't match char_type, the function calls os.widen (c) before inserting the character. Before returning, the function calls os.width (0).

template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, const charT* s);
template<class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, const char* s); 
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os, const char* s);
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os, unsigned char* s);
template<class traits>
basic_ostream<char, traits>&
operator<<(basic_ostream<char, traits>& os, signed char* s);

After constructing a sentry object the function inserts traits::length(s) characters starting at s plus any required padding into os. Characters starting at s are widened by calling os.widen (*s). Before returning, the function calls os.width (0).

The formatting is done through member functions or manipulators.

Table 11: Formatting manipulators and functions for basic_ostream 

The meaning of the manipulators is as follows:

showpos	Generates a + sign in nonnegative 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 unconditionally in generated floating-point output
boolalpha	Inserts and extracts the 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 notation
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 parameter 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 width (number of characters) to generate on certain output conversions

//
//  ostream1.cpp
//

#include <iostream>   // for cout, endl, hex, oct
#include <sstream>    // for istringstream
#include <iomanip>    // for setfill, setprecision, setw


int main ( )
{
    // create a read/write stringbuf object on tiny char
    // and attach it to an istringstream object
    std::istringstream in (std::ios::in | std::ios::out);
      
    // tie the ostream object to the istringstream object
    std::ostream out (in.rdbuf ());

    out << "test beginning !" << std::endl;

    // output an int value in hexadecimal
    const int i = 22;
    out << std::hex << i << std::endl; 

    // set the field width to 10, the padding character 
    // to '@' and output i in octal notation
    out << std::setw (10) << std::oct 
        << std::setfill ('@') << i << std::endl;

    // output a float with precision set to 2 digits 
    // after the separator
    const float f = 3.14159123;
    out << std::setprecision (3) << f << std::endl;

    const char s[] = "Why, one can hear the grass growing!";

    // output the 17 first characters of s
    out.write (s, 17);

    // output a newline character
    out.put ('\n');

    // output s 
    out << s << std::endl;   

    // output the entire contents of the buffer 
    // to standard output
    std::cout << in.rdbuf();

    return 0;
}


Program Output:

test beginning !
16
@@@@@@@@26
3.14
Why, one can hear
Why, one can hear the grass growing!

//
//  ostream2.cpp
//
 
#include <iostream>   // for wcout, endl
#include <sstream>    // for wistringstream



int main ()
{
    const float f = 3.14159;

    const wchar_t s[] = { 'K', 'e', 'n', 'a', 'v', 
                          'o', ' ', '!', '\0' };

    // create a read/write stringbuf object on wide char
    // and attach it to an wistringstream object
    std::wistringstream in (std::wios::in | std::wios::out);
      
    // tie the wostream object to the wistringstream object
    std::wostream out (in.rdbuf ());

    out << L"test beginning !" << std::endl;
    out.setf (std::wios::fixed, std::wios::floatfield);

    // output f in fixed format
    out << f << std::endl; 

    // store the current put-pointer position  
    std::wostream::pos_type pos = out.tellp ();

    // output s 
    out << s << std::endl;

    // output the all buffer to standard output
    std::wcout << in.rdbuf () << std::endl;

    // position the get-pointer
    in.seekg (pos);

    // output s
    std::wcout << in.rdbuf () << std::endl;         

    return 0;
}


Program Output:

test beginning !
3.141593
Kenavo !

Kenavo !

char_traits, ios_base, basic_ios, basic_streambuf, basic_iostream

ISO/IEC 14882:1998 -- International Standard for Information Systems --Programming Language C++, Section 27.6.2.1