C++ template class with boost signals2

Question

I'm trying to use the boost signals and slots with C++ templates. Here is the example code:

#include <iostream>
#include <sstream>
#include <string>

#include <boost/signals2/signal.hpp>

template<class T>
class JBase
{
public:
    JBase(T &d) : data(d)
    {}
    virtual ~JBase() {}
    virtual bool DoSomething(std::string &outStr) = 0;

protected:
T data;
};

class LToUse : public JBase<int>
{
public:
   LToUse(int d) : JBase<int>(d) {}
   virtual ~LToUse() {}
   bool DoSomething(std::string &outStr)
   {
      std::ostringstream s;
      s << data;
      outStr = s.str();
      return true;
   }
};

template<class T>
typedef boost::signals2::signal<void(const JBase<T> &jsonObj)>::slot_type Sig_t;

class CBHndlr
{
   CBHndlr()
   {
      // I get errors even on this line...??
      //Sig_t t = boost::bind(&CBHndlr::TestCb, this, _1);
      //m_Signal.connect(t)
   }

   template<class T>
   void TestCb(JBase<T> *obj)
   {

   }

private:
   template<class T>
   boost::signals2::signal<void(JBase<T>)> m_Signal;
};

template<class T>
void TestJL(JBase<T> *obj)
{
   std::string s;
   obj->DoSomething(s);
   std::cout << "Did Something: " << s;
}

When I compile, I get (compilation) errors saying:

typedef template is illegal
syntax error : missing ';' before identifier 'Sig_t'

Are there any restrictions on using boost signals with templates? FYI - I'm not using C++11.

Any suggestions/help is much appreciated.

`template boost::signals2::signal)> m_Signal;` is an illegal member too. — Jarod42, Aug 14 '14 at 15:11

Jarod42 · Accepted Answer · 2014-08-14T15:33:10.297

2

template typedef is illegal, but you may use using in C++11:

template<class T>
using Sig_t = typename boost::signals2::signal<void(const JBase<T> &jsonObj)>::slot_type;

In C++03,

you may encapsulate inside a struct:

template <typename T>
struct Sig
{
    typedef typename boost::signals2::signal<void(const JBase<T> &jsonObj)>::slot_type type;
};

And then use Sig<T>::type.

EDIT: The following may help you:

template <typename T>
class CBHndlr
{
   CBHndlr()
   {
      typename Sig<T>::type t = boost::bind(&CBHndlr::TestCb, this, _1);
      m_Signal.connect(t)
   }

   void TestCb(JBase<T> *obj) {}
private:
   boost::signals2::signal<void(JBase<T>)> m_Signal;
};

edited Aug 14 '14 at 15:33

answered Aug 14 '14 at 15:05

Jarod42

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Thanks for the quick response. As mentioned in the post, I'm not using C++11. Isn't 'using' a C++ 11 feature? – user3605077 Aug 14 '14 at 15:07
@user3605077: I edited the answer for an alternative with C++03. – Jarod42 Aug 14 '14 at 15:08
Thanks. Based on Jarod42's [@user3605077] comment, I wrapped the typedef within a struct, but I'm still getting compilation errors. Can you show me in the example CBHndlr() class how to actually declare it and connect the signal/slot? Again - thanks for the help/suggestion. – user3605077 Aug 14 '14 at 15:25

score 0 · Answer 2 · answered Aug 14 '14 at 15:06

Your problem is as you quoted typedef template is illegal. It is, you cannot have a template typedef, and it does not have much to do with boost::signals.

In C++11 they introduced type aliases which you may use instead

template<class T> using Sig_t = <your type>

C++ template class with boost signals2

2 Answers2