c++ - 控制多线程程序中的输出流

Question

我正在尝试控制模拟中的输出打印。它打印了很多输出流信息。这是我如何尝试控制输出流的示例代码。有时我想为每个线程打印信息，有时我不想从线程中打印一次以减少模拟中的系统调用。我通过命令行参数来控制流。争论v意味着没有指纹。问题是它在整个模拟器中需要很多if语句。有没有简单的方法来处理这个问题？

#include <iostream>
#include <thread>

void work_to_do_1(char ch)
{
//work for thread 1
if(ch != 'v')
std::cout << "-:Thread 1:-" << std::endl;
}

void work_to_do_2(char ch)
{
if (ch != 'v')
std::cout << "-:Thread 2:-" << std::endl;
}

void work_to_do_3(char ch)
{
if (ch != 'v')
std::cout << "-:Thread 3:-" << std::endl; 
}

int main(int argc, char *arg[])
{
std::cout << "You have entered " << argc
    << " arguments:" << "\n";

for (int i = 0; i < argc; ++i)
{
    std::cout << arg[i] << "\n";
}
char t = *arg[1];
std::cout << "manager is running" << std::endl;

std::thread t1(work_to_do_1, t);
std::thread t2(work_to_do_2, t);
std::thread t3(work_to_do_3, t);
t1.join();
t2.join();
t3.join();
system("pause");
return 0;
}

标签： c++multithreading

Answer 1

Make your own nul stream:

struct cnul_t : std::basic_ostream<char> {} cnul;
template<class T> std::ostream& operator<<(cnul_t& os, T const&) { return os; }

And redirect your output to it to ignore it:

#include <ostream>
#include <iostream>

struct cnul_t : std::basic_ostream<char> {} cnul;
template<class T> std::ostream& operator<<(cnul_t& os, T const&) { return os; }

void maybe_log(bool b)
{
    std::ostream& out = b == true ? std::cout : cnul;
    out << "Hello, World!\n";
}

int main()
{
    maybe_log(true);  // outputs Hello, World!
    maybe_log(false); // no output
}

Demo: http://coliru.stacked-crooked.com/a/362ecb660283cbff