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

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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_osyncstream
 
basic_osyncstream( streambuf_type* buf, const Allocator& a );
 (1)
explicit basic_osyncstream( streambuf_type* buf );
 (2)
basic_osyncstream( std::basic_ostream<CharT, Traits>& os, const Allocator& a );
 (3)
explicit basic_osyncstream( std::basic_ostream<CharT, Traits>& os );
 (4)
basic_osyncstream( std::basic_osyncstream&& other ) noexcept;
 (5)

Constructs new synchronized output stream

1-4) constructs the private member std::basic_syncbuf using the buffer and the allocator provided, and initializes the base class with a pointer to the member std::basic_streambuf.
5) Move constructor. Move-constructs the std::basic_ostream base and the std::basic_syncbuf member from the corresponding subobjects of other, then calls set_rdbuf with the pointer to the newly-constructed underlying std::basic_syncbuf to complete the initialization of the base. After this move constructor, other.get_wrapped() returns nullptr and destruction of other produces no output.

Parameters

buf - pointer to the std::basic_streambuf that will be wrapped
os - reference to a std::basic_ostream, whose rdbuf() will be wrapped
a - the allocator to pass to the constructor of the member std::basic_syncbuf
other - another osyncstream to move from

Example

Run this code
#include <string_view>
#include <syncstream>
#include <iostream>
#include <thread>
 
void worker(const int id, std::ostream &os) {
  std::string_view block;
  switch (id) {
    default: [[fallthrough]];
    case 0: block = "██"; break;
    case 1: block = "▓▓"; break;
    case 2: block = "▒▒"; break;
    case 3: block = "░░"; break;
  }
  for(int i = 1; i <= 50; ++i) {
    os << block << std::flush;
  }
  os << std::endl;
}
 
int main() {
  std::cout << "Synchronized output should not cause any interference:" << std::endl;
  {
    auto scout1 = std::osyncstream{std::cout};
    auto scout2 = std::osyncstream{std::cout};
    auto scout3 = std::osyncstream{std::cout};
    auto scout4 = std::osyncstream{std::cout};
    auto w1 = std::jthread{worker, 0, std::ref(scout1)};
    auto w2 = std::jthread{worker, 1, std::ref(scout2)};
    auto w3 = std::jthread{worker, 2, std::ref(scout3)};
    auto w4 = std::jthread{worker, 3, std::ref(scout4)};
  }
 
  std::cout << "\nLack of synchronization may cause some interference on output:" << std::endl;
  {
    auto w1 = std::jthread{worker, 0, std::ref(std::cout)};
    auto w2 = std::jthread{worker, 1, std::ref(std::cout)};
    auto w3 = std::jthread{worker, 2, std::ref(std::cout)};
    auto w4 = std::jthread{worker, 3, std::ref(std::cout)};
  }
}

Possible output: 

Synchronized output should not cause any interference:
░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░░
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████████████████████████████████████████████████████████████████████████████████████████████████████
 
Lack of synchronization may cause some interference on output:
████▓▓██▒▒▒▒▓▓██░░▒▒██░░▒▒░░░░▒▒░░▓▓▒▒██░░████████████▓▓██████▓▓▒▒▓▓██░░████▓▓▓▓██▒▒░░░░░░░░▓▓░░▓▓██▒▒▒▒▒▒▒▒▓▓██▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒░░▒▒▒▒░░▒▒▒▒▒▒▒▒▒▒▓▓▒▒▒▒▒▒▒▒▒▒▒▒██░░░░░░░░▓▓▓▓▓▓▓▓▓▓▓▓▓▓░░▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓████████▓▓▓▓▓▓▓▓▓▓▓▓░░▓▓▓▓
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See also

 constructs a basic_syncbuf object
(public member function of std::basic_syncbuf<CharT,Traits,Allocator>)
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