std::basic_ostringstream::basic_ostringstream(3)

NAME
std::basic_ostringstream::basic_ostringstream - std::basic_ostringstream::basic_ostringstream

Synopsis
   explicit basic_ostringstream( std::ios_base::openmode mode = (until C++11)
                        std::ios_base::out );
   explicit basic_ostringstream( std::ios_base::openmode mode ); (since C++11)
   basic_ostringstream() (2) (since C++11)
       : basic_ostringstream(std::ios_base::out) {}
   explicit basic_ostringstream
       ( const std::basic_string<CharT, Traits, Allocator>& str, (3)
         std::ios_base::openmode mode =
             std::ios_base::out );
   explicit basic_ostringstream
       ( std::basic_string<CharT, Traits, Allocator>&& str, (4) (since C++20)
         std::ios_base::openmode mode =
             std::ios_base::out );
   basic_ostringstream( std::ios_base::openmode mode, const (5) (since C++20)
   Allocator& a );
   template< class SAlloc >
   basic_ostringstream( const std::basic_string<CharT, Traits,
   SAlloc>& str, (6) (since C++20)
                        std::ios_base::openmode mode, const
   Allocator& a );
   template< class SAlloc >
   basic_ostringstream( const std::basic_string<CharT, Traits, (1)
   SAlloc>& str, (7) (since C++20)
                        const Allocator& a )
       : basic_ostringstream(str, std::ios_base::out, a) {}
   template< class SAlloc >
   explicit basic_ostringstream
       ( const std::basic_string<CharT, Traits, SAlloc>& str, (8) (since C++20)
         std::ios_base::openmode mode =
             std::ios_base::out );
   template< class StringViewLike >
   explicit basic_ostringstream
       ( const StringViewLike& t, (9) (since C++26)
         std::ios_base::openmode mode =
             std::ios_base::out );
   template< class StringViewLike >
   basic_ostringstream( const StringViewLike& t, (10) (since C++26)
                        std::ios_base::openmode mode, const
   Allocator& a );
   template< class StringViewLike >
   basic_ostringstream( const StringViewLike& t, const (11) (since C++26)
   Allocator& a );
   basic_ostringstream( basic_ostringstream&& other ); (12) (since C++11)
   Constructs new string stream.
   Given
     * base_type as std::basic_ostream<CharT, Traits>, and
     * buf_type as std::basic_stringbuf<CharT, Traits, Allocator>,
   the std::basic_ostream base and the exposition-only data member sb are initialized
   as follows.
    Over std::basic_ostream base sb
    load
   (1) buf_type(mode | std::ios_base::out)
   (2) buf_type(std::ios_base::out)
   (3) buf_type(str, mode |
                        std::ios_base::out)
   (4) buf_type(std::move(str), mode |
                        std::ios_base::out)
   (5) base_type(std::addressof(sb))^[1] buf_type(mode | std::ios_base::out,
                        a)
   (6) buf_type(str, mode |
                        std::ios_base::out, a)
   (7) buf_type(str, std::ios_base::out,
                        a)
   (8) buf_type(str, mode |
                        std::ios_base::out)
   (9) {t, mode | std::ios_base::out,
          std::addressof(sb) Allocator()}
   (10) {t, mode | std::ios_base::out, a}
   (11) {t, std::ios_base::out, a}
   (12) move constructed from other's move constructed from other.sb
          std::basic_ostream base
    1. ↑ The std::basic_iostream base was intialized with base_type(&sb) (for overloads
       (1,3)) until C++11.
   8) This overload participates in overload resolution only if std::is_same_v<SAlloc,
   Allocator> is false.
   9-11) These overloads participate in overload resolution only if
   std::is_convertible_v<const StringViewLike&, std::basic_string_view<CharT, Traits>>
   is true.

Parameters
   str - string to use as initial contents of the string stream
   t - an object (convertible to std::basic_string_view) to use as initial contents
           of the string stream
   a - allocator used for allocating the contents of the string stream
           specifies stream open mode. It is a BitmaskType, the following constants are
           defined:
           Constant Explanation
           app seek to the end of stream before each write
   mode - binary open in binary mode
           in open for reading
           out open for writing
           trunc discard the contents of the stream when opening
           ate seek to the end of stream immediately after open
           noreplace (C++23) open in exclusive mode
   other - another string stream to use as source

Notes
   Construction of one-off basic_ostringstream objects in a tight loop, such as when
   used for string conversion, may be significantly more costly than calling str() to
   reuse the same object.
           Feature-test macro Value Std Feature
   __cpp_lib_sstream_from_string_view 202306L (C++26) Interfacing std::stringstreams
                        with std::string_view, (9-11)

Example
// Run this code
 #include <iostream>
 #include <sstream>
 int main()
 {
     // default constructor (input/output stream)
     std::stringstream buf1;
     buf1 << 7;
     int n = 0;
     buf1 >> n;
     std::cout << "buf1 = " << buf1.str() << " n = " << n << '\n';
     // input stream
     std::istringstream inbuf("-10");
     inbuf >> n;
     std::cout << "n = " << n << '\n';
     // output stream in append mode (C++11)
     std::ostringstream buf2("test", std::ios_base::ate);
     buf2 << '1';
     std::cout << buf2.str() << '\n';
 }

Output:
 buf1 = 7 n = 7
 n = -10
 test1
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
     DR Applied to Behavior as published Correct behavior
   P0935R0 C++11 the default constructor was explicit made implicit

See also
   str gets or sets the contents of underlying string device object
                 (public member function)
                 constructs a basic_stringbuf object
   constructor (public member function of
                 std::basic_stringbuf<CharT,Traits,Allocator>)