C++ Function pointer map with Class Member Variables

Question

I am trying to make a stl map with key as "KEYWORD" and value as "Class member function" But it is not getting compiled. Following is the code. Can anybody please let me know what is wrong. The class member functions are not static.

typedef void (RemoteHostManager::*CmdHandlerPtr)(char *);
typedef std::map<char *,CmdHandlerPtr> CommandHandlerSet;
typedef std::map<char *,CmdHandlerPtr>::iterator CommandHandlerSetItr;

void RemoteHostManager::InitializeCmdHandlerMap()
{
    m_CommandSet["HELP"]    = &RemoteHostManager::usage;
    m_CommandSet["CONNECT"] = &RemoteHostManager::Connect;
    m_CommandSet["READ"]    = &RemoteHostManager::Read;
    m_CommandSet["WRITE"]   = &RemoteHostManager::Write;
    m_CommandSet["STOP"]    = &RemoteHostManager::Stop;
    m_CommandSet["START"]   = &RemoteHostManager::Start;
}

Following are the errors:

RemoteHostManager.cpp: In member function `void
   RemoteHostManager::InitializeCmdHandlerMap()':
RemoteHostManager.cpp:14: no match for `std::_Rb_tree_iterator<std::pair<const
   std::string, void (RemoteHostManager::*)(char*)>, std::pair<const
   std::string, void (RemoteHostManager::*)(char*)>&, std::pair<const
   std::string, void (RemoteHostManager::*)(char*)>*>& [const char[5]]'
   operator
//similar error for other assignments!

the problem is it is getting compiler or it is NOT getting compiled? — Naveen
– Naveen, Commented Jan 18, 2011 at 6:44
@Avinash : what is the type of m_CommandSet?.. and tell us line number corresponds to which piece of code.. by the way, have you changed char* to std::string in the map? — Sarfaraz Nawaz
– Sarfaraz Nawaz, Commented Jan 18, 2011 at 7:18
So, what's m_CommandSet? You posted a bunch of typedef's, yet the most important part - the declaration of m_CommandSet - is missing. — AnT stands with Russia
– AnT stands with Russia, Commented Jan 18, 2011 at 7:19
@Avinash : I guess, the type of m_CommandSet is not CommandHandlerSet; it's rather CommandHandlerSetItr.Am I right? — Sarfaraz Nawaz
– Sarfaraz Nawaz, Commented Jan 18, 2011 at 7:22
@Nawaz and @AndreyT, you got it right, my m_commandSet was wrong. — Avinash
– Avinash, Commented Jan 18, 2011 at 7:23

Sarfaraz Nawaz · Accepted Answer · 2011-01-18 07:04:59Z

3

typedef std::map<char *,CmdHandlerPtr> CommandHandlerSet;
typedef std::map<char *,CmdHandlerPtr>::iterator CommandHandlerSetItr;

First make it const char*, or even better std::string:

typedef std::map<std::string,CmdHandlerPtr> CommandHandlerSet;
typedef std::map<std::string,CmdHandlerPtr>::iterator CommandHandlerSetItr;

Note all your member functions should match the type of CmdHandlerPtr. That is, the parameter type must be char* , and return type must be void.

When using the map, you need an instance of type RemoteHostManager:

RemoteHostManager instance;
string key;
//...
(instance.*m_CommandSet[key])(param);

edited Jan 18, 2011 at 7:04

answered Jan 18, 2011 at 6:43

Sarfaraz Nawaz

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1 Comment

Avinash Over a year ago

Thanks, But I am getting error at line m_CommandSet["HELP"] = &RemoteHostManager::usage; and usage memeber function is defined as void RemoteHostManager::usage( char *inCmd)

Eric Fortin · Accepted Answer · 2011-01-18 06:50:11Z

1

If class member functions are not static, you need to bind the method with an instance when setting it in the map. You could use boost::bind to do so.

answered Jan 18, 2011 at 6:50

Eric Fortin

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2 Comments

Potatoswatter Over a year ago

What? Not with the syntax he's using. Also that would change the program from what he wants to do. Please read up on pointer-to-member-function variables.

Eric Fortin Over a year ago

On which instance will it call the method then if the methods aren't static ?

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