A TCP port scanner in 'C'

This is a simple port scanner coded in c. It uses a simple socket and a for loop. The port scanner uses TCP Connect to check whether the port is opened or closed.

This is for beginners who are trying to grasp simple sockets in C.

By the way this is for linux platform you can easily compile this on win32 using cygwin.


/* A TCP port scanner created by billy www.softhardware.co.uk*/

#include < stdio.h >
#include < sys/types.h >
#include < sys/socket.h >
#include < netinet/in.h >
#include < netdb.h >
#include < stdlib.h >
#include < errno.h >

/* Main programs starts*/
int main(int argc, char **argv)
{
   int   sd;         //socket descriptor
   int    port;         //port number
   int   start;         //start port
   int    end;         //end port
   int    rval;         //socket descriptor for connect  
   char    responce[1024];      //to receive data
   char   *message="shell";       //data to send
   struct hostent *hostaddr;   //To be used for IPaddress
   struct sockaddr_in servaddr;   //socket structure  
   if (argc < 4 )
   {
      printf("------Created By www.Softhardware.co.uk-----------\n");
      printf("--------------------------------------------------\n");
      printf("Usage: ./tscan   \n");
      printf("--------------------------------------------------\n");
      return (EINVAL);
   }
   start = atoi(argv[2]);
   end   = atoi(argv[3]);
   for (port=start; port<=end; port++)
   {         //portno is ascii to int second argument    
   sd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP); //created the tcp socket
   if (sd == -1)
   {
     perror("Socket()\n");
     return (errno);
   }  
   memset( &servaddr, 0, sizeof(servaddr));
   servaddr.sin_family = AF_INET;
   servaddr.sin_port = htons(port); //set the portno  
   hostaddr = gethostbyname( argv[1] ); //get the ip 1st argument  
   memcpy(&servaddr.sin_addr, hostaddr->h_addr, hostaddr->h_length);    
   //below connects to the specified ip in hostaddr
   rval = connect(sd, (struct sockaddr *) &servaddr, sizeof(servaddr));
   if (rval == -1)
   {
   printf("Port %d is closed\n", port);
   close(sd);
   }
   else
   printf("Port %d is open\n",port);  
   close(sd);         //socket descriptor
   }  
}


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