Re: Getting access to std::map value (a struct)

"Angus" <>
Sun, 1 Oct 2006 23:39:59 +0100
If I use insert, as in:

m_AgentsList.insert( std::make_pair(deviceID, thisagent));

Then get error:

SocketServer.cpp(524) : error C2663: 'insert' : 3 overloads have no legal
conversion for 'this' pointer

This time using the CAgents as below:

class CAgents





m_Socket = 0;

m_dwDeviceID = 0;

// m_strLogin = TEXT("");

}; // default constructor - init values to sensible defaults

CAgents(const Socket* pSocket, const DWORD DeviceID, const std::string&


m_Socket = pSocket;

m_dwDeviceID = DeviceID;

m_strLogin = strLogin;


CAgents(const CAgents& rhs)

:m_Socket(rhs.GetSocket()), m_dwDeviceID(rhs.GetDeviceID()),

{}; // assign rhs = eg

const Socket* m_Socket; // ptr to socket for client

DWORD m_dwDeviceID; // (DeviceID) extn

std::string m_strLogin; // logon

DWORD GetDeviceID() const


return m_dwDeviceID;


std::string GetLogin() const


return m_strLogin;


const Socket* GetSocket() const


return m_Socket;


CAgents& operator=(const CAgents& rhs)


m_Socket = rhs.GetSocket();

m_dwDeviceID = rhs.GetDeviceID();

m_strLogin = rhs.GetLogin();

return *this;




"Angus" <> wrote in message


And one last question. How do I assign a agents to m_AgentsList?

I tried m_AgentsList[4] = thisagent;

But got
error C2678:

binary '[' : no operator defined which takes a left-hand operand of type
'const class std::map<int,class CSocketServer
::CAgents,struct std::less<int>,class std::allocator<class
CSocketServer::CAgents> >' (or there is no acceptable conversion)


"Alex Blekhman" <xfkt@oohay.moc> wrote in message

"Angus" <> wrote in message


I am struggling here with a std::map like this:

struct agents
 Socket* agentsocket; // ptr to socket for client
 DWORD dwDeviceID; // (DeviceID)
 char szLogon[100]; // logon
agents thisagent;
thisagent.agentsocket = 0;
thisagent.dwDeviceID = 6;
lstrcpy(thisagent.szLogon, "Angus");
agents thatagent;
thatagent.agentsocket = 0;
thatagent.dwDeviceID = 8;
lstrcpy(thatagent.szLogon, "Lisa");
// std::map<Key,Val>:
std::map<int, agents> m_AgentsList;
m_AgentsList[4] = thisagent;
m_AgentsList[8] = thatagent;

So if I want to get access to the agents in
m_AgentsList[4] I would do this:
agents myagent = m_AgentsList[4]; // compile error line
std::cout << myagent.szLogon << std::endl;
Easy enough. This compiles in my test program. But if I
compile in my main
program I get this:
SocketServer.cpp(410) :
error C2678:
binary '[' : no operator defined which takes a left-hand
operand of type
'const class std::map<int,struct CSocketServe
r::agents,struct std::less<int>,class
CSocketServer::agents> >' (or there is no acceptable

I have exactly the same code in SocketServer.cpp as my
test code in a really
small test cpp file.

You cannot call `std::map::operator[]' on constant instance
of map. It happens because `std::map::operator[]'

    a) can change map instance
    b) returns non-const reference to contained object.

If you need to search for value on constant map instance,
then use `std::map::find' method:

std::map<int, agents>::const_iterator it =

if(it != m_AgentsList.end())
    const agents& a = it->second;

    std::cout << a.szLogon << std::endl;

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