Re: socket bind always returns 0, why?

From:

oxkfame@gmail.com

Newsgroups:

comp.lang.c++

Date:

Wed, 28 May 2014 08:11:02 -0700 (PDT)

Message-ID:

<743b18b1-e48d-4f2a-93ba-73540b12f0eb@googlegroups.com>

Thanks, I've changed it to LOOPBACK, but it didn't change anything. I still see two bindings in netstat:
[./]$ sudo netstat -lptu |grep 1908
tcp 0 0 localhost:19080 *:* LISTEN 12273/Test
tcp 0 0 localhost:19080 *:* LISTEN 12273/Test

On Tuesday, May 27, 2014 7:45:32 PM UTC-5, Geoff wrote:

On Tue, 27 May 2014 10:27:58 -0700 (PDT), oxkfame@gmail.com wrote:

The following code returns 0 from the bind, even when netstat clearly shows that the port is taken by another process, ie the following function will always return true. Why?

bool isPortAvailable( int port )

       {

           SOCKET candidateSocket;

           if(( candidateSocket = socket( AF_INET, SOCK_STREAM, 0 )) == -1 )

               return false;

           struct sockaddr_in serverAddress;

           memset (&serverAddress, 0, sizeof (serverAddress));

           serverAddress.sin_family = AF_INET;

           serverAddress.sin_addr.s_addr = htonl( INADDR_ANY );

           serverAddress.sin_port = htons( port );

           if( ::bind( candidateSocket, (struct sockaddr*)&serverAddress, sizeof( serverAddress )) != 0 )

           {

               closesocket( candidateSocket );

               return false;

           }

           closesocket( candidateSocket );

           return true;

       }

My first guess would be that the other process has the port on a

distinct IP address, your bind is to INADDR_ANY. This would let your

process have a port listening on 0.0.0.0:port which, IIRC, is distinct

from another process listening on 127.0.0.1:port for example. To prove

this guess correct, use the same IP address to which the other process

is bound and see if this function fails.

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