std::basic_...stringstream(3)

🎀 std::basic_...stringstream(3) — C++ Standard Libary, section 3 🎀

okay bestie, this is the C++ Standard Libary manual page for std::basic_ostringstream::basic_ostringstream, and we're gonna make it make sense. no cap. 💅

💖 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 );
(1) (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.

• (1) — base: (empty); sb: buf_type(mode | std::ios_base::out)
• (2) — base: (empty); sb: buf_type(std::ios_base::out)
• (3) — base: (empty); sb: buf_type(str, mode | std::ios_base::out)
• (4) — base: (empty); sb: buf_type(std::move(str), mode | std::ios_base::out)
• (5) — base: base_type(std::addressof(sb))^[1]; sb: buf_type(mode | std::ios_base::out, a)
• (6) — base: (empty); sb: buf_type(str, mode | std::ios_base::out, a)
• (7) — base: (empty); sb: buf_type(str, std::ios_base::out, a)
• (8) — base: (empty); sb: buf_type(str, mode | std::ios_base::out)
• (9) — base: std::addressof(sb); sb: {t, mode | std::ios_base::out, Allocator()}
• (10) — base: (empty); sb: {t, mode | std::ios_base::out, a}
• (11) — base: (empty); sb: {t, std::ios_base::out, a}
• (12) — base: move constructed from other's std::basic_ostream base; sb: 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:
  • 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:

• __cpp_lib_sstream_from_string_view — value 202306L; Std (C++26); feature: 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.

• P0935R0 — Applied to: C++11; Behavior as published: the default constructor was explicit; Correct behavior: made implicit

🌈 See also 🌈

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

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