getaddrinfo() help please
Results 1 to 3 of 3

Thread: getaddrinfo() help please

  1. #1
    Senior Member
    Join Date
    Apr 2002
    Posts
    161

    getaddrinfo() help please

    Hi, I am currently trying to write a program that takes two arguments from the command line. The first one is the IP address (xxx.xxx.xx.xx) or hostname (whatever.edu), the second argument is the port number. I am writing a simple TCP client/server application in C and want to be able to use either the numerical form of and address or the actual name. In order to convert a hostname to an address I will use getaddrinfo(). My problem comes with my second argument, since I want to use any port number and not the name of the service specified by well known ports.

    Example: ./tcpclient it.abc.edu 12345

    From: man getaddrinfo

    Code:
    int
         getaddrinfo(const char *nodename, const char *servname,
                 const struct addrinfo *hints, struct addrinfo **res);
    As you can see the second argument is a string that identifies the service, I will not be implementing any service in well known ports. When getaddrinfo returns, it returns a pointer to a linked list of addrinfo structs. Within this structs there is a pointer to a socket address structure, which is filled by getaddrinfo. Is there anyway to overwrite the values pointed at by this pointer to a sockaddr structure?? Because then I could:

    Code:
    getaddrinfo( address, NULL, &hints, &results);
    Making the service argument NULL, and then somehow modifying the port value in the returned socket address structure.
    And then make the proper calls to socket() and connect().

    I hope its not too confusing
    thnx
    J

  2. #2
    Custom User
    Join Date
    Oct 2001
    Posts
    503
    A quick google search would have done the trick:

    http://hpcf.nersc.gov/vendor_docs/ib...etaddrinfo.htm

    If you look at the description part of the page, it says that the second argument is either a service name or a decimal port number. You should be able to simply do some error checking on argv[2] to make sure that it's a number (probably doesn't really matter too much) and feed it into the function:

    Code:
    getaddrinfo(address, argv[2], &hints, &results);
    ac

  3. #3
    Senior Member
    Join Date
    Apr 2002
    Posts
    161
    Yep, that's it, the second argument can be a number. I don't recommend coding for long periods without taking breaks, coz then you get frustrated and don't see that your errors are simply fixed. That is exactly what happened to me here.

    peace always
    J

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •