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

std::basic_ostringstream<CharT,Traits,Allocator>::basic_ostringstream - cppreference.com

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	(1)
`explicit basic_ostringstream( std::ios_base::openmode mode = {{#pad:\|28}} 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, {{#pad:\|19}} 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, {{#pad:\|19}} 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, {{#pad:\|19}} 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

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 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`

↑ 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

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

Parameters

Notes

Example

Defect reports

See also