Simple C/C++ port scanner.

gistfile1.cpp

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

int main(int argc, char** argv) {
  for (size_t port = 0; port < 1024; port++) {
    // Set up info for the getaddrinfo request
    char sport[10];
    // Connect to this port number
    sprintf(sport, "%zu", port);
    struct addrinfo hints = {0};
    // Use either IPv4 or IPv6, we're OK with either.
    hints.ai_family = AF_UNSPEC;
    // Must be TCP. connect() doesn't tell us anything for a UDP 'connection'.
    hints.ai_socktype = SOCK_STREAM;

    // Retrieve address info's. If this returns failure, you probably mistyped the address or domain name.
    struct addrinfo* addr;
    if (getaddrinfo(argv[1], sport, &hints, &addr) != 0) {
      printf("Target host could not be looked up");
      return -1;
    }

    // Assuming we get here, we'll connect to the first result coming out.
    // Normally you'd retry to the other results from getaddrinfo, but 
    // 1. I'm lazy and 
    // 2. we actually want the error message more.
    int sock = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
    int res = connect(sock, addr->ai_addr, addr->ai_addrlen);

    // If it failed, check what kind of failure to determine the state of the port
    if (res == -1) {
      switch(errno) {
        case ETIMEDOUT:
          printf("Port %zu is shadowed\n", port);
          break;
        case ECONNREFUSED:
          printf("Port %zu is closed\n", port);
          break;
        case ENETUNREACH:
          printf("Cannot reach the target host\n");
          return -1;
      }
    // Otherwise, I guess it worked.
    } else {
      printf("Port %zu is open\n", port);
    }

    // Clean up and go back for another port connect attempt.
    close(sock);
    freeaddrinfo(addr);
  }
  return 0;
}