使用ios_base::register_callback()和ios_base::event检测流关闭

我有一个API，它向API用户返回一个unique_ptr<ofstream>。我想知道用户什么时候完成这个流，这样我就可以对他们刚刚写入的文件采取进一步的操作。因为要重新挂载一个分区，所以必须关闭该文件。

这可能是这个问题的错误解决方案，但是在我返回流之前，我用register_callback()注册了一个回调:

std::unique_ptr<std::ofstream> os(new std::ofstream(name, std::ofstream::out | std::ofstream::trunc | std::ofstream::binary));
os->register_callback(done_callback, 0);
return os;

回调在别处定义:

void done_callback(std::ios_base::event evt, std::ios_base& str, int idx)
{
    // Do something when the file closes ... and only then.
}

现在，ios_base::event告诉回调函数刚刚发生了什么。其中一个事件是erase_event，该事件的触发器之一是销毁流对象。这对我有用。我关心的是触发回调的另一个条件——copyfmt()。

• 我应该担心这个还是相信没有人会引起要调用Copyfmt()吗?
有没有更好的方法来完成我的目标?

这是我用来测试的源代码(完整，剪切/粘贴)，然后是该程序的输出:

#include <iostream>
#include <fstream>
#include <memory>
void done_callback(std::ios_base::event evt, std::ios_base& str, int idx)
{
    std::cout << "Some sort of stream event occurred. Event: " << evt << std::endl;
}
int main(int argc, char* argv[]) {
    std::cout << "Opening the stream." << std::endl;
    std::unique_ptr<std::ofstream> os(new std::ofstream("test", std::ofstream::out | std::ofstream::trunc | std::ofstream::binary));
    std::cout << "Stream is open." << std::endl;
    std::cout << "Registering callback." << std::endl;
    os->register_callback(done_callback, 0);
    std::cout << "Writing to stream." << std::endl;
    *(os.get()) << "Hello!n";
    std::cout << "Done writing." << std::endl;
    std::cout << "Flushing stream." << std::endl;
    os->flush();
    std::cout << "Done flushing." << std::endl;
    std::cout << "Writing to stream." << std::endl;
    *(os.get()) << "Hello!n";
    std::cout << "Done writing." << std::endl;
    std::cout << "Closing the stream..." << std::endl;
    os->close();
    std::cout << "Stream is closed." << std::endl;
}

输出:

Opening the stream.
Stream is open.
Registering callback.
Writing to stream.
Done writing.
Flushing stream.
Done flushing.
Writing to stream.
Done writing.
Closing the stream...
Stream is closed.
Some sort of stream event occurred. Event: 0