Aaron Conole

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C Programming Tutorial

C-Network application

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <unistd.h>

int main(int argc, char** argv){
     int sd, rc, i;
     struct sockaddr_in localAddr, servAddr;
     struct hostent *h;

     if(argc < 4){
          printf("Useage: %s <machine to scan> <start port> <end port>\n", argv[0]);
          exit(0);
     }

     h = gethostbyname(argv[1]);
     if(h == NULL){
          printf("%s: unknown host: %s", argv[0], argv[1]);
          exit(0);
     }

     for ( i = atoi(argv[2]); i < atoi(argv[3]); i++){
          servAddr.sin_family = h->h_addrtype;
          memcpy((char *) &servAddr.sin_addr.s_addr, h->h_addrlist[0], h->h_length);
          servAddr.sin_port = htons(i);

          sd = socket(AF_INET, SOCK_STREAM, 0);
          if(sd < 0){
               perror("%s: error cannot open socked\n", argv[0]);
               exit(1);
          }

          localAddr.sin_family = AF_INET;
          localAddr.sin_addr.s_addr = htonl(INADDR_ANY);
          localAddr.sin_port = htons(0);

          rc = bind(sd, (struct sockaddr *) &localAddr, sizeof(localAddr));
          if (rc < 0) {
               printf("%s: cannot bind port TCP %u", argv[0], i);
               perror("Error..cannot bind to port!");
               exit(1);
          }

          rc = connect(sd, (struct sockaddr *) &servAddr, sizeof(servAddr));

          if ( rc >= 0 ) {
               printf("%s: %s accepting on port %u\n", argv[0], argv[1], i);
          }

          close(sd);
     }

     return 0;
}