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std::basic_ostringstream<CharT,Traits,Allocator>::basic_ostringstream

(1) 
explicit basic_ostringstream( std::ios_base::openmode mode =
                                  std::ios_base::out );
 (until C++11) 
explicit basic_ostringstream( std::ios_base::openmode mode );
 (since C++11) 
basic_ostringstream()
    : basic_ostringstream(std::ios_base::out) {}
 (2) (since C++11) 
explicit basic_ostringstream
    ( const std::basic_string<CharT, Traits, Allocator>& str,
      std::ios_base::openmode mode =
          std::ios_base::out );
 (3) 
explicit basic_ostringstream
    ( std::basic_string<CharT, Traits, Allocator>&& str,
      std::ios_base::openmode mode =
          std::ios_base::out );
 (4) (since C++20) 
basic_ostringstream( std::ios_base::openmode mode, const Allocator& a );
 (5) (since C++20) 
template< class SAlloc >
basic_ostringstream( const std::basic_string<CharT, Traits, SAlloc>& str,
                     std::ios_base::openmode mode, const Allocator& a );
 (6) (since C++20) 
template< class SAlloc >
basic_ostringstream( const std::basic_string<CharT, Traits, SAlloc>& str,
                     const Allocator& a )
    : basic_ostringstream(str, std::ios_base::out, a) {}
 (7) (since C++20) 
template< class SAlloc >
explicit basic_ostringstream
    ( const std::basic_string<CharT, Traits, SAlloc>& str,
      std::ios_base::openmode mode =
          std::ios_base::out );
 (8) (since C++20) 
template< class StringViewLike >
explicit basic_ostringstream
    ( const StringViewLike& t,
      std::ios_base::openmode mode =
          std::ios_base::out );
 (9) (since C++26) 
template< class StringViewLike >
basic_ostringstream( const StringViewLike& t,
                     std::ios_base::openmode mode, const Allocator& a );
 (10) (since C++26) 
template< class StringViewLike >
basic_ostringstream( const StringViewLike& t, const Allocator& a );
 (11) (since C++26) 
basic_ostringstream( basic_ostringstream&& other );
 (12) (since C++11)

Constructs new string stream.

Given

the std::basic_ostream base and the exposition-only data member sb are initialized as follows.

Over
load		 std::basic_ostream base sb
(1) base_type(std::addressof(sb))[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) 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) std::addressof(sb) {t, mode | std::ios_base::out, Allocator()}
(10) {t, mode | std::ios_base::out, a}
(11) {t, std::ios_base::out, a}
(12) move constructed from other's std::basic_ostream base move constructed from other.sb
  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
mode - 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
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

#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

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

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