C socket programming no port entered

Question

I'm trying to set a default port number for when no port is entered in C socket programming. Does anyone know how I can do this? I keep getting segmentation fault on attempts.

Code:

#define PORT 12345

int main(int argc, char *argv[]) {

    /* Thread and thread attributes */
    pthread_t client_thread;
    pthread_attr_t attr;


    int sockfd, new_fd;  /* listen on sock_fd, new connection on new_fd */
    struct sockaddr_in my_addr;    /* my address information */
    struct sockaddr_in their_addr; /* connector's address information */
    socklen_t sin_size;
    int i=0;

    /* Get port number for server to listen on */
    if (argc != 2) {
        fprintf(stderr,"usage: client port_number\n");
        exit(1);
    }

    /* generate the socket */
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        exit(1);
    }

    /* generate the end point */
    my_addr.sin_family = AF_INET;         
    my_addr.sin_port = htons(atoi(argv[1]));     
    my_addr.sin_addr.s_addr = INADDR_ANY; 

I tried setting the default to 12345 when argc != 2, but I get segmentation fault. Any help would be appreciated!

Answer 1

You can use a conditional expression.

#define DEFAULT_PORT 12345
my_addr.sin_port = htons(argc < 2 ? DEFAULT_PORT : atoi(argv[1]));