Getting error C2440: char[]* to char* (pointers)

Question

(Obvious beginner in c++, keep struggling with pointers)

I've been trying to get the IP address of the client as the server (using TCP), and to save it using a pointer to be able to re-use it later.

In a previous function, I accept the connection and save the Socket as m_clientSocket and the Socket information in a struct sockaddr called clientaddr.

Now, I want the next function to return the client socket and to save the source IP, but the program keeps crashing.

In this last version, I've tried to use a pointer but there's an error in conversion that I can't fix despite my researches.

char clientIPaddr[30];
sockaddr_in clientaddr;
SOCKET m_clientSocket;

Function code

SOCKET CmTcpListener::getNewSocket(SOCKET *hSocket, char* ptrSourceIp) 
{
    cout << "Retrieving socket..." << endl;
    if (m_newClientConnection)
    {
        hSocket = &m_clientSocket;

        strcpy(clientIPaddr, inet_ntoa(clientaddr.sin_addr));

        ptrSourceIp = &clientIPaddr;

        cout << "Socket : OK" << endl;

        return *hSocket;
    }
    else {
        cout << "No new client connection." << endl;
        return false;
    }

}

Error

c:\work\2015\tcptransport\cmtcplistener.cpp(112) : error C2440: '=' : cannot convert from 'char (*)[30]' to 'char *' Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

I'm assuming the rest of the code isn't necessary but if needed I'll be quick to provide it

Answer 1

The culprit is the line

ptrSourceIp = &clientIPaddr;

clientIPaddr is of type char[30], so the type of &clientIPaddr is char(*)[30], i.e. pointer to array of 30 chars. Remove the & and you'll be OK, as the name of the array is itself a pointer to its first element (technically, arrays decay to pointers)

ptrSourceIp = clientIPaddr;

However, right now, you're not doing anything with ptrSourceIp, at the end of the function will be unchanged since it is passed by value like any other variable. If you want to modify the passed pointer ptrSourceIp, then you need to pass a pointer to it (i.e. a pointer-to-pointer-to-char), so the prototype of your function should be:

SOCKET CmTcpListener::getNewSocket(SOCKET *hSocket, char** ptrSourceIp) 

The second argument you pass has to be &your_passed_ptr_to_char. Inside your function you can now modify the passed pointer like

*ptrSourceIp = clientIpAddr; // now we modify it