TCP Port Scanner In C Programming

tcp-port-scanner.c

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

#define MAX_PORT 65535

void error(const char *msg)
{
    perror(msg);
    exit(1);
}

int main(int argc, char *argv[])
{
    int sockfd, port;
    struct sockaddr_in serv_addr;
    struct hostent *server;

    if (argc < 2) {
        fprintf(stderr, "Usage: %s <hostname>\n", argv[0]);
        exit(1);
    }

    server = gethostbyname(argv[1]);
    if (server == NULL) {
        fprintf(stderr, "Error: Unable to resolve hostname\n");
        exit(1);
    }

    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(80);
    memcpy(&serv_addr.sin_addr, server->h_addr, server->h_length);

    for (port = 1; port <= MAX_PORT; port++) {
        sockfd = socket(AF_INET, SOCK_STREAM, 0);
        if (sockfd < 0) {
            error("Error: Unable to create socket");
        }

        serv_addr.sin_port = htons(port);

        if (connect(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) == 0) {
            printf("Port %d is open\n", port);
        }

        close(sockfd);
    }

    return 0;
}