使用 boost::bind ...我做错了什么

Question

我改编了以下问题的第一个答案中的代码来制作周期性计时器： How do I make the boost/asio library repeat a timer?

我删除了 "count" 变量，因为我想重复执行的方法不采用任何参数进行计算。

编译失败并出现以下错误：

Error   C2825   'F': must be a class or namespace when followed by '::' C:\.conan\wkypad\include\boost\bind\bind.hpp  75  
Error   C2510   'F': left of '::' must be a class/struct/union  C:\.conan\wkypad\include\boost\bind\bind.hpp  75  
Error   C3646   'type': unknown override specifier  C:\.conan\wkypad\include\boost\bind\bind.hpp  75  
Error   C4430   missing type specifier - int assumed. Note: C++ does not support default-int C:\.conan\wkypad\include\boost\bind\bind.hpp 75  
Error   C2039   'type': is not a member of 'boost::_bi::result_traits<R,F>' C:\.conan\wkypad\include\boost\bind\bind.hpp  1284

我做错了什么？我想我对 boost::bind 的用法是错误的，但我无法找出确切原因。

这是我的代码的相关部分

class ProjectBrowserComponent ...

private:
    void fetchData(const boost::system::error_code& /*e*/,
        boost::asio::deadline_timer* t);
    std::vector<Project> projects;
    ProjectsController pc;
    std::future<std::vector<Project>> projectsFuture;
    int interval_secs = 1;

...

template<typename R>
bool isReady(std::future<R> const& f)
{
    Logger::writeToLog("check future");
    return f.wait_for(std::chrono::seconds(-1)) == std::future_status::ready;
}

void ProjectBrowserComponent::initData() {
    Logger::writeToLog("requesting projects");
    projectsFuture = std::async(std::launch::async, &ProjectsController::getProjects, &pc);
    Logger::writeToLog("requested projects");
    boost::asio::io_service io_service;
    boost::asio::deadline_timer timer(io_service, boost::posix_time::seconds(interval_secs));
    timer.async_wait(boost::bind(&ProjectBrowserComponent::fetchData, boost::asio::placeholders::error, &timer));
    io_service.run();
}

void ProjectBrowserComponent::fetchData(const boost::system::error_code& /*e*/,
    boost::asio::deadline_timer* timer) {
    if (isReady(projectsFuture)) {
        projects = projectsFuture.get();
        std::cout << "got projs";
    }
    else {
        timer->expires_at(timer->expires_at() + boost::posix_time::seconds(interval_secs));
        // Posts the event
        timer->async_wait(boost::bind(&ProjectBrowserComponent::fetchData, boost::asio::placeholders::error, timer));
    }
}

Answer 1

这个怎么样：

timer.async_wait(boost::bind(&ProjectBrowserComponent::fetchData, this, boost::asio::placeholders::error, &timer));

如果绑定成员函数，则还必须将它们绑定到 class 对象的正确实例。在这里，我将其绑定到 this，从代码的外观来看，我认为这是您正在做的事情。

sehe 来自评论的注释：

请务必注意，这必须在整个异步操作期间保持有效。实现此目的的一种流行方法是使 ProjectBrowserComponent 继承自 enable_shared_from_this 并绑定到 shared_from_this()

使用 boost::bind ...我做错了什么

Usage of boost::bind ... what am I doing wrong

c++

boost

compiler-errors

timer

boost-bind