lsof-lite.c

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <errno.h>

typedef struct sockaddr *sad; /* A necesary dummy typedef */

#define PORT 48006

int main()
{
	int sock; /* Socket that will be bind */
	struct sockaddr_in sin; /* Address Structure */
	
	/* Create the socket */
	/* PF_INET is the option for make a TCP socket.
		 You can try "man socket" for more info */
	sock = socket( PF_INET, SOCK_STREAM, 0 );
	
	/* The socket creation failed */
	if ( 0 > sock ) {
		perror( "socket" );
		return ( -1 );
	}
	
	/* Address */
	sin.sin_family = AF_INET;
	sin.sin_port = htons( PORT ); /* htons() convert the number
                                                      to big endian */
	sin.sin_addr.s_addr = INADDR_ANY;
	
	/* We bind the socket to the port PORT to check if
           the port is in use */
	if ( 0 > bind( sock, (sad)&sin, sizeof( sin ) ) ) {
		/* Bind failed, now we can check if the address is
                 in use */

		if ( EADDRINUSE == errno ) {
			/* We put the code necesary to manage this case */
			printf( "The TCP port %d is in use.\n", PORT );
		}

		else
		/* If the error were other than EADDRINUSE, we print it */
		perror( "bind" );
	}
	
	/* If we arrive to this point, the port weren't in use and
          we have it attached to our program. We can close
          the socket or use it */
	close( sock ); /* Close the socket */
	
	return 0;
}