boost:bind的函数类型不对

[icooperlee]

Channel.h

class Channel : boost::noncopyable
{
public:
typedef boost::function<void()> EventCallback;
typedef boost::function<void(Timestamp)> ReadEventCallback;

Channel(EventLoop* loop, int fd);
~Channel();

void handleEvent(Timestamp receiveTime);
void setReadCallback(const ReadEventCallback& cb)
{ readCallback = cb; }
void setWriteCallback(const EventCallback& cb)
{ writeCallback_ = cb; }
void setCloseCallback(const EventCallback& cb)
{ closeCallback_ = cb; }
void setErrorCallback(const EventCallback& cb)
{ errorCallback_ = cb; }

EventLoop.cc

EventLoop::EventLoop()
: looping_(false),
quit_(false),
eventHandling_(false),
callingPendingFunctors_(false),
iteration_(0),
threadId_(CurrentThread::tid()),
poller_(Poller::newDefaultPoller(this)),
timerQueue_(new TimerQueue(this)),
wakeupFd_(createEventfd()),
wakeupChannel_(new Channel(this, wakeupFd_)),
currentActiveChannel_(NULL)
{
LOG_TRACE << "EventLoop created " << this << " in thread " << threadId_;
if (t_loopInThisThread)
{
LOG_FATAL << "Another EventLoop " << t_loopInThisThread
<< " exists in this thread " << threadId_;
}
else
{
t_loopInThisThread = this;
}
wakeupChannel->setReadCallback(
boost::bind(&EventLoop::handleRead, this));
// we are always reading the wakeupfd
wakeupChannel_->enableReading();
}

EventLoop::handleRead函数是没有参数的，而ReadEventCallback是带Timestamp参数的，这二者不匹配。

[chenshuo]

This is not a bug.

It's a feature of boost::bind and std::bind, as stated in its document [1]:

Any extra arguments are silently ignored,

[1] https://www.boost.org/doc/libs/1_73_0/libs/bind/doc/html/bind.html

[icooperlee]

Thank you very much. But i still don't understand, and this is a test.

mybind.c

#include <stdio.h>
#include <boost/bind.hpp>
#include <boost/function.hpp>

typedef boost::function<void(int)> CallbackFun;

void myprint()
{
    printf("myprint...\n");
}

int main()
{
    CallbackFun f;
    f = boost::bind(myprint);
    f();

    return 0;
}

---

$ g++ mybind.c -o bind
mybind.c: In function ‘int main()’:
mybind.c:17:7: error: no match for call to ‘(CallbackFun {aka boost::function<void(int)>}) ()’
f();
^
In file included from /usr/include/boost/function/detail/maybe_include.hpp:22:0,
from /usr/include/boost/function/detail/function_iterate.hpp:14,
from /usr/include/boost/preprocessor/iteration/detail/iter/forward1.hpp:52,
from /usr/include/boost/function.hpp:70,
from mybind.c:3:
/usr/include/boost/function/function_template.hpp:1048:7: note: candidate is:
class function<BOOST_FUNCTION_PARTIAL_SPEC>
^
/usr/include/boost/function/function_template.hpp:758:17: note: boost::function1<R, T1>::result_type boost::function1<R, T1>::operator()(T0) const [with R = void; T0 = int; boost::function1<R, T1>::result_type = void]
result_type operator()(BOOST_FUNCTION_PARMS) const

[icooperlee]

Sorry, i have a mistake. Should be like this.

#include <stdio.h>
#include <boost/bind.hpp>
#include <boost/function.hpp>


typedef boost::function<void(int)> CallbackFun;

void myprint()
{
    printf("myprint...\n");
}

int main()
{
    CallbackFun f;
    f = boost::bind(myprint);
    f(1);

    return 0;
}

[chenshuo]

What's the question here? The code works just fine: https://ideone.com/Mhjl02

#include <stdio.h>
#include <functional>
 
using Callback = std::function<void(int)>;
 
void print() {
	printf("Hello\n");
}
 
int main() {
	Callback f = std::bind(print);
	f(43);  // prints "Hello"
	return 0;
}

[icooperlee]

Now, I understand that is not a bug. Can you tell me why it works well? Thanks. "f = boost::bind(myprint); // ok. why ?"

#include <stdio.h>
#include <boost/bind.hpp>
#include <boost/function.hpp>


typedef boost::function<void(int)> CallbackFun;

typedef void (*pFun)(int);


void myprint()
{
    printf("myprint...\n");
}


int main()
{
    CallbackFun f;
    f = boost::bind(myprint); // ok.   why ?
    f(1); // ok

    pFun pf = boost::bind(myprint); // complie error 

    return 0;
}