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

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C++
 
Input/output library
I/O manipulators
C-style I/O
Buffers
(C++23)
(deprecated in C++98)
(C++20)
Streams
Abstractions
File I/O
String I/O
Array I/O
(C++23)
(C++23)
(C++23)
(deprecated in C++98)
(deprecated in C++98)
(deprecated in C++98)
Synchronized Output
(C++20)
Types
Error category interface
(C++11)
(C++11)
 
std::basic_ostringstream
Member functions
basic_ostringstream::basic_ostringstream
(C++11)
String operations
(C++20)
Non-member functions
(C++11)
 
basic_ostringstream()
    : basic_ostringstream(std::ios_base::out) { }
 (1) (since C++11)
(2)
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)
explicit basic_ostringstream( const std::basic_string<CharT,Traits,Allocator>& str,
                              std::ios_base::openmode mode = std::ios_base::out );
 (3)
basic_ostringstream( basic_ostringstream&& other );
 (4) (since C++11)
basic_ostringstream( std::ios_base::openmode mode, const Allocator& a );
 (5) (since C++20)
explicit basic_ostringstream( std::basic_string<CharT,Traits,Allocator>&& str,
                              std::ios_base::openmode mode = std::ios_base::out );
 (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>

basic_ostringstream( const std::basic_string<CharT,Traits,SAlloc>& str,

                     std::ios_base::openmode mode, const Allocator& a );
 (8) (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 );
 (9) (since C++20)

Constructs new string stream.

1) Default constructor. Constructs new underlying string device with the default open mode
2) Constructs new underlying string device. The underlying basic_stringbuf object is constructed as basic_stringbuf<Char,Traits,Allocator>(mode | std::ios_base::out).
3) Uses a copy of str as initial contents of the underlying string device. The underlying basic_stringbuf object is constructed as basic_stringbuf<Char,Traits,Allocator>(str, mode | std::ios_base::out).
4) Move constructor. Constructs the string stream with the state of other using move semantics.
5) Constructs new underlying string device. The underlying basic_stringbuf object is constructed as basic_stringbuf<Char,Traits,Allocator>(mode | std::ios_base::out, a).
6) Move-construct the contents of the underlying string device with str. The underlying basic_stringbuf object is constructed as basic_stringbuf<Char,Traits,Allocator>(std::move(str), mode | std::ios_base::out).
7) Constructs new underlying string device. The underlying basic_stringbuf object is constructed as basic_stringbuf<Char,Traits,Allocator>(str, std::ios_base::out, a).
8) Constructs new underlying string device. The underlying basic_stringbuf object is constructed as basic_stringbuf<Char,Traits,Allocator>(str, mode | std::ios_base::out, a).
9) Constructs new underlying string device. The underlying basic_stringbuf object is constructed as basic_stringbuf<Char,Traits,Allocator>(str, mode | std::ios_base::out). This overload participates in overload resolution only if SAlloc and Allocator are not the same type.

Parameters

str - string 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 bitmask type, 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
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.

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 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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