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

From cppreference.net
C++
Input/output library
std::basic_osyncstream
Public member functions
basic_osyncstream::basic_osyncstream
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
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)

构造新的同步输出流。

1-4) 使用提供的缓冲区和分配器构造私有成员 std:: basic_syncbuf ，并使用指向该成员的指针初始化基类 std:: basic_streambuf 。
5) 移动构造函数。从 other 的对应子对象移动构造 std:: basic_ostream 基类和 std::basic_syncbuf 成员，随后调用 set_rdbuf 并传入新构造的底层 std:: basic_syncbuf 指针以完成基类的初始化。在此移动构造函数执行后， other. get_wrapped ( ) 将返回 nullptr ，且 other 的析构不会产生任何输出。

参数

buf - 指向将被包装的 std::basic_streambuf 的指针
os - 对 std::basic_ostream 的引用，其 rdbuf() 将被包装
a - 传递给成员 std::basic_syncbuf 构造函数的分配器
other - 用于移动来源的另一个 osyncstream

示例

运行此代码 
#include <iostream>
#include <string_view>
#include <syncstream>
#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)};
    }
}

可能的输出： 

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

构造 basic_syncbuf 对象
( std::basic_syncbuf<CharT,Traits,Allocator> 的公开成员函数)