如何将sockaddr结构转换为sockaddr_in - C ++网络套接字ubuntu UDP

Question

I am trying to get the client address, but i am unsure how do i cast the sockaddr structure to sockaddr_in?

struct sockaddr_in cliAddr, servAddr;

    n = recvfrom(sd, msg, MAX_MSG, 0,(struct sockaddr *) cliAddr,sizeof(cliAddr));

 //i tried this but it does not work
    struct sockaddr cliSockAddr = (struct sockaddr *) cliAddr; 
    char *ip = inet_ntoa(cliSockAddr.sin_addr);

Thanks in advance! :)

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i've found questions that brought me to this step: Getting IPV4 address from a sockaddr structure

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Sorry to avoid confusion, this is my real implementation where "ci" is an object to store pointers such as sockaddr_in.

    /* receive message */
    n = recvfrom(*(ci->getSd()), msg, MAX_MSG, 0,(struct sockaddr *) ci->getCliAddr(),ci->getCliLen());

    char *ip = inet_ntoa(ci->getCliAddr().sin_addr);

i will get the following errors:

udpserv.cpp:166: error: request for member ‘sin_addr’ in ‘ci->clientInfo::getCliAddr()’, which is of non-class type ‘sockaddr_in*’

Answer 1

I would point out that if this is actually C++ the idiomatic way to do this would be:

sockaddr *sa = ...; // struct not needed in C++
char ip[INET6_ADDRSTRLEN] = {0};

switch (sa->sa_family) {
  case AF_INET: {
    // use of reinterpret_cast preferred to C style cast
    sockaddr_in *sin = reinterpret_cast<sockaddr_in*>(sa);
    inet_ntop(AF_INET, &sin->sin_addr, ip, INET6_ADDRSTRLEN);
    break;
  }
  case AF_INET6: {
    sockaddr_in6 *sin = reinterpret_cast<sockaddr_in6*>(sa);
    // inet_ntoa should be considered deprecated
    inet_ntop(AF_INET6, &sin->sin6_addr, ip, INET6_ADDRSTRLEN);
    break;
  }
  default:
    abort();
}

This sample code handles IPv4 and IPv6 addresses and also would be considered more C++ idiomatic than either of the suggested implementations.

Answer 2

It is actually very simple!

struct sockaddr *sa = ...;

if (sa->sa_family == AF_INET)
{
    struct sockaddr_in *sin = (struct sockaddr_in *) sa;
    ip = inet_ntoa(sin->sin_addr);
}

Answer 3

I think this will compile just fine for you and do what you want.

struct sockaddr_in cliAddr={}, servAddr={};

socklen_t cliAddrLength = sizeof(cliAddr);

n = recvfrom(sd, msg, MAX_MSG, 0,(struct sockaddr *)&cliAddr, &cliAddrLength);