'不匹配'與成員回調函數使用std :: tr1 :: function的錯誤

Question

我想創建一個回調函數使用str :: tr1 ::函數指向一個公共成員函數。

std::tr1::function < int (const string& , const MessageInfo* , const void* , const int , const void*) > dssCallBack; 
dssCallBack = &ABC::mDBtoDScallback; 

該回調函數將傳遞給另一個ABC類函數體內的函數。的ABC::mDBtoDScallback簽名是

int DataserviceSubscriber::mDBtoDScallback(const string& strTopic, const MessageInfo* messageInfo, const void* data, const int dataLen, const void* callback_data) 

當我嘗試編譯此，我給G收到以下錯誤++。

In file included from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1/functional:56, 
       from ../src/bmrk/databus/ABC.hpp:17, 
       from ../src/bmrk/databus/ABC.cpp:1: 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional: In static member function ‘static _Res std::tr1::_Function_handler<_Res(_ArgTypes ...), _Member _Class::*>::_M_invoke(const std::tr1::_Any_data&, _ArgTypes ...) [with _Class = ABC, _Member = int(const std::string&, const MessageInfo*, const void*, int, const void*), _Res = int, _ArgTypes = const std::string&, const MessageInfo*, const void*, int, const void*]’: 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:2005: instantiated from ‘std::tr1::function<_Res(_ArgTypes ...)>::function(_Functor, typename __gnu_cxx::__enable_if<(! std::tr1::is_integral::value), std::tr1::function<_Res(_ArgTypes ...)>::_Useless>::__type) [with _Functor = int (ABC::*)(const std::string&, const MessageInfo*, const void*, int, const void*), _Res = int, _ArgTypes = const std::string&, const MessageInfo*, const void*, int, const void*]’ 

/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:1885: instantiated from ‘typename __gnu_cxx::__enable_if<(! std::tr1::is_integral::value), std::tr1::function<_Res(_ArgTypes ...)>&>::__type std::tr1::function<_Res(_ArgTypes ...)>::operator=(_Functor) [with _Functor = int (ABC::*)(const std::string&, const MessageInfo*, const void*, int, const void*), _Res = int, _ArgTypes = const std::string&, const MessageInfo*, const void*, int, const void*]’ 
../src/bmrk/databus/dataservice_subscriber.cpp:266: instantiated from here 

/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:1714: error: no match for call to ‘(std::tr1::_Mem_fn<int (ABC::*)(const std::string&, const MessageInfo*, const void*, int, const void*)>) (const std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, const MessageInfo*&, const void*&, int&, const void*&)’ 

/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:546: note: candidates are: _Res std::tr1::_Mem_fn<_Res (_Class::*)(_ArgTypes ...)>::operator()(_Class&, _ArgTypes ...) const [with _Res = int, _Class = ABC, _ArgTypes = const std::string&, const MessageInfo*, const void*, int, const void*] 

/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:551: note:     _Res std::tr1::_Mem_fn<_Res (_Class::*)(_ArgTypes ...)>::operator()(_Class*, _ArgTypes ...) const [with _Res = int, _Class = ABC, _ArgTypes = const std::string&, const MessageInfo*, const void*, int, const void*] 

我想看看我在這裏做錯了，但無法發現它。我試圖查找，但找不到其他類似問題的人。我可以使用C風格的typedef，但我想使用和保留C++風格，在這個過程中也習慣了C++ 11中的一些新的東西。

謝謝。

編輯：根據要求由邁克爾·伯爾，回叫正在從一個函數調用按這裏http://en.cppreference.com/w/cpp/utility/functional/function

int ABC::subs_rt(const vector<string> &symbols, raw_callback_t raw_callback, void *app_data, Error *error) 
{ 
    DBtoDS_callback_data cbData; 
    cbData.subscriber_callback = raw_callback; 
    cbData.raw_callback_app_data = app_data; 
    cbData.err = error; 

    // Perform processing on 'symbols' 
    // dss is a member of class ABC and has been initialized in constructor 
    dss->AddSubscriptionPrefix(symbols); 
    b_cancel_subscription = false; 

    std::tr1::function < int (const string& , const MessageInfo* , const void* , const int , const void*) > dssCallBack; 
    dssCallBack = &DataserviceSubscriber::mDBtoDScallback; 

    dss->Subscribe(dssCallBack, static_cast<const void*>(&cbData)); 

    return 0; 
} 

參考回調本身看起來像

int ABC::mDBtoDScallback(const string& strTopic, const MessageInfo* messageInfo, const void* data, const int dataLen, const void* callback_data) 
{ 
    const DBtoDS_callback_data* cbData = static_cast<const DBtoDS_callback_data*>(callback_data); 

    if(0 == messageInfo) // Version 1 
    { 
     // Do callback Stuff 
    } 
    else // Version 2 
    { 
     Subscriber::timeval_t now; 
     TimeUtils::now(now); 
     std::string payload(static_cast<const char*>(data), dataLen); 

     // Do callback Stuff 
    } 
} 

功能int ABC::mDBtoDScallback是不像WhozCraig猜測的那樣是靜態的。那是問題嗎？我不能使這個函數中使用的一些變量是靜態的。有沒有辦法解決這個問題，還是我必須使用C風格的函數指針？

謝謝。

編輯2：根據n.m.和WhozCraig的關注和每此鏈接C++: Assigning a function to a tr1::function object

我在ABC更改的行:: subs_rt功能

std::tr1::function < int (const string& , const MessageInfo* , const void* , const int , const void*) > dssCallBack; 
//dssCallBack = std::tr1::bind(&ABC::mDBtoDScallback, this, std::tr1::placeholders::_1); 
dssCallBack = std::tr1::bind(&ABC::mDBtoDScallback, this); 

我嘗試了評論和註釋掉的選擇，但現在我得到這個錯誤

In file included from /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1/functional:56, 
       from ../src/bmrk/databus/ABC.hpp:17, 
       from ../src/bmrk/databus/ABC.cpp:1: 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional: In member function ‘typename std::tr1::result_of<_Functor(typename std::tr1::result_of<std::tr1::_Mu<_Bound_args, std::tr1::is_bind_expression::value, (std::tr1::is_placeholder::value > 0)>(_Bound_args, std::tr1::tuple<_UElements ...>)>::type ...)>::type std::tr1::_Bind<_Functor(_Bound_args ...)>::__call(const std::tr1::tuple<_UElements ...>&, std::tr1::_Index_tuple<_Indexes ...>) [with _Args = const std::basic_string<char, std::char_traits<char>, std::allocator<char> >&, const MessageInfo*&, const void*&, int&, const void*&, int ..._Indexes = 0, _Functor = std::tr1::_Mem_fn<int (ABC::*)(const std::string&, const MessageInfo*, const void*, int, const void*)>, _Bound_args = ABC*]’: 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:1191: instantiated from ‘typename std::tr1::result_of<_Functor(typename std::tr1::result_of<std::tr1::_Mu<_Bound_args, std::tr1::is_bind_expression::value, (std::tr1::is_placeholder::value > 0)>(_Bound_args, std::tr1::tuple<_UElements ...>)>::type ...)>::type std::tr1::_Bind<_Functor(_Bound_args ...)>::operator()(_Args& ...) [with _Args = const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, const MessageInfo*, const void*, int, const void*, _Functor = std::tr1::_Mem_fn<int (ABC::*)(const std::string&, const MessageInfo*, const void*, int, const void*)>, _Bound_args = ABC*]’ 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:1654: instantiated from ‘static _Res std::tr1::_Function_handler<_Res(_ArgTypes ...), _Functor>::_M_invoke(const std::tr1::_Any_data&, _ArgTypes ...) [with _Res = int, _Functor = std::tr1::_Bind<std::tr1::_Mem_fn<int (ABC::*)(const std::string&, const MessageInfo*, const void*, int, const void*)>(ABC*)>, _ArgTypes = const std::string&, const MessageInfo*, const void*, int, const void*]’ 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:2005: instantiated from ‘std::tr1::function<_Res(_ArgTypes ...)>::function(_Functor, typename __gnu_cxx::__enable_if<(! std::tr1::is_integral::value), std::tr1::function<_Res(_ArgTypes ...)>::_Useless>::__type) [with _Functor = std::tr1::_Bind<std::tr1::_Mem_fn<int (ABC::*)(const std::string&, const MessageInfo*, const void*, int, const void*)>(ABC*)>, _Res = int, _ArgTypes = const std::string&, const MessageInfo*, const void*, int, const void*]’ 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:1885: instantiated from ‘typename __gnu_cxx::__enable_if<(! std::tr1::is_integral::value), std::tr1::function<_Res(_ArgTypes ...)>&>::__type std::tr1::function<_Res(_ArgTypes ...)>::operator=(_Functor) [with _Functor = std::tr1::_Bind<std::tr1::_Mem_fn<int (ABC::*)(const std::string&, const MessageInfo*, const void*, int, const void*)>(ABC*)>, _Res = int, _ArgTypes = const std::string&, const MessageInfo*, const void*, int, const void*]’ 
../src/bmrk/databus/ABC.cpp:266: instantiated from here 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:1137: error: no match for call to ‘(std::tr1::_Mem_fn<int (ABC::*)(const std::string&, const MessageInfo*, const void*, int, const void*)>) (ABC*&)’ 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:546: note: candidates are: _Res std::tr1::_Mem_fn<_Res (_Class::*)(_ArgTypes ...)>::operator()(_Class&, _ArgTypes ...) const [with _Res = int, _Class = ABC, _ArgTypes = const std::string&, const MessageInfo*, const void*, int, const void*] 
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/tr1_impl/functional:551: note:     _Res std::tr1::_Mem_fn<_Res (_Class::*)(_ArgTypes ...)>::operator()(_Class*, _ArgTypes ...) const [with _Res = int, _Class = ABC, _ArgTypes = const std::string&, const MessageInfo*, const void*, int, const void*] 
make[1]: *** [ABC.lo] Error 1 

問題的解決方案：鑑於我的要求決定讓我的回調成爲一個靜態成員函數並通過const void* callback_data傳遞一個指向父類對象的指針。作爲一個靜態函數，它可以訪問ABC類的私有函數並將參數傳遞給raw_callback。我從所有評論中獲得的幫助對我來說都是一次重大的學習經歷，並最終讓我朝着解決方案邁進。

static int ABC::mDBtoDScallback(const string& strTopic, const MessageInfo* messageInfo, const void* data, const int dataLen, const void* callback_data) 
{ 
    const DBtoDS_callback_data* cbData = static_cast<const DBtoDS_callback_data*>(callback_data); 

    TimeUtils::now(now); 
    std::string payload(static_cast<const char*>(data), dataLen); 

    string symbol; 
    string sym; 
    int pri_s = 0; 

    if(0 == messageInfo) 
    { 
     parse_topic(strTopic, symbol, pri_s, cbData->err); 
    } 
    else 
    { 
     symbol = messageInfo->key(); 
     pri_s = (messageInfo->has_pri_s() ? messageInfo->pri_s() : 0); 
    } 
    if (cbData->subs->symbols_need_translation()) 
    { 
     cbData->subs->translate_symbol(cbData->subs->_translator, symbol, sym, false); 
    } 
    else 
    { 
     sym = symbol; 
    } 

    cbData->subscriber_callback(cbData->subs, sym, pri_s, cbData->subs->prod, payload, now, cbData->raw_callback_app_data, cbData->err); 
} 

謝謝。

Answer 1

正如評論中所討論的，問題似乎是因爲你的函數對象期望一個靜態的非對象綁定函數，而你實際上將它傳遞給了一個成員。從我所看到的情況來看，有幾種解決方法，這是你可能已經考慮過的最簡單的方法;使用靜態並將對象的指針作爲參數傳遞。

或者，我不知道這是否適用於您的特定體系結構，但以下內容快速捕捉瞭如何使用std::mem_fn<>與std::function<>一起使用指定對象調用成員函數。這是一個獨立的樣本，但我希望你能看到它是如何幫助你的。

#include <iostream> 
#include <functional> 
using namespace std; 

class MyClass 
{ 
public: 
    MyClass() {} 

    int CallMe(void *p, int a, float f) 
    { 
     // use params herere 
     cout << "CallMe fired : " << this << " !\n" << endl; 
     return 0; 
    } 
}; 

int main() 
{ 
    MyClass obj, obj2; 
    std::function<int(MyClass*,void*,int,float)> fn(std::mem_fn(&MyClass::CallMe)); 

    cout << "Invoking CallMe with " << &obj << " object..." << endl; 
    fn(&obj, NULL, 1, 2.0); 

    cout << "Invoking CallMe with " << &obj2 << " object..." << endl; 
    fn(&obj2, NULL, 1, 2.0); 

    return 0; 
} 

輸出

Invoking CallMe with 0x7fff5fbff7d8 object... 
CallMe fired : 0x7fff5fbff7d8 ! 

Invoking CallMe with 0x7fff5fbff7d0 object... 
CallMe fired : 0x7fff5fbff7d0 ! 

注意

的成員函數對象的方式工作，提供了C++ 11，上cppreference.com是迷人給我讀。並不是說任何人真的關心這一點。我不知道他們是否適當地派遣到虛擬等，但我對他們感到非常驚訝。

我希望你覺得這很有幫助，但如果其中一位真正瞭解std :: function，std :: bind和std :: men_fn pony的std-lib專家完全準備好將其刪除提供更簡潔的解釋（或將此片段撕成碎片）。老實說，在SO的某處通過std::function<>調用成員可能會有更好的樣本，但使用std::men_fn<>與std::function<>的簡單性我不得不說很迷人。

---

虛擬調度

尋求DeadMG的評論我是真的好奇，如果虛擬調度工作後。我認爲這是一個很好的機會，因爲我們提供了一個this指針，但並沒有屏住呼吸，因爲我們顯然通過了MyClass::CallMe成員的地址給我們的std:::mem_fn<>的構造函數。

更新後的源代碼和生成的運行很有趣。注意兩個實例中使用的相同的函數對象。無論它是否打算以這種方式工作（它似乎，順便說一句）我不能說，但我感到很有趣，無論如何。

#include <iostream> 
#include <functional> 
using namespace std; 

class MyClass 
{ 
public: 
    MyClass() {} 

    virtual int CallMe(void *p, int a, float f) 
    { 
     // use params herere 
     cout << "MyClass::CallMe fired : " << this << endl; 
     return 0; 
    } 
}; 

class MyDerived : public MyClass 
{ 
public: 
    MyDerived() {} 

    virtual int CallMe(void *p, int a, float f) 
    { 
     // use params herere 
     cout << "MyDerived::CallMe fired : " << this << endl; 
     return 0; 
    } 
}; 

int main() 
{ 
    MyClass obj; 
    MyDerived obj2; 

    std::function<int(MyClass*,void*,int,float)> fn(std::mem_fn(&MyClass::CallMe)); 

    cout << "Invoking CallMe with " << &obj << " object..." << endl; 
    fn(&obj, NULL, 1, 2.0); 

    cout << "Invoking CallMe with " << &obj2 << " object..." << endl; 
    fn(&obj2, NULL, 1, 2.0); 

    return 0; 
} 

輸出

Invoking CallMe with 000000000021FB58 object... 
MyClass::CallMe fired : 000000000021FB58 
Invoking CallMe with 000000000021FB78 object... 
MyDerived::CallMe fired : 000000000021FB78 

Answer 2

來源很簡單，如果你知道去哪裏找。考慮下面的代碼：

std::tr1::function < int (const string& , const MessageInfo* , const void* , const int , const void*) > dssCallBack; 
dssCallBack = &ABC::mDBtoDScallback; 
dssCallBack(std::string(), nullptr, nullptr, 0, nullptr); 

什麼是this？你從來沒有提供過。所以std::function不可能使這個工作 - 你試圖調用一個成員，但沒有提供一個對象。什麼是std::function應該做的，神奇地決定什麼this應該是什麼？

這兩種解決方案是使用std::bind綁定this，或者通過this作爲參數，如std::mem_fn。