get the socket type (TCP / UDP)

socktype.c

#include <stdio.h>
#include <sys/socket.h>

int opt = -1;
socklen_t optlen = sizeof(opt);

int main(int argc, char **argv)
{
	int type;

    if (argc != 2) {
        printf("%s <tcp / udp>\n", argv[0]);
        return -1;
    }

	if (!strcasecmp(argv[1], "tcp")) {
		type = SOCK_STREAM;
	} else if (!strcasecmp(argv[1], "udp")) {
		type = SOCK_DGRAM;
	} else {
		printf("%s <tcp / udp>\n", argv[0]);
		return -1;
	}

	int sock;

	sock = socket(AF_INET, type, 0);
	if (sock < 0) {
		return -1;
	}

	int ret;

	ret = getsockopt(sock, SOL_SOCKET, SO_TYPE, &opt, &optlen);
	if (ret < 0) {
		close(sock);
		return -1;
	}

    close(sock);
	printf("sock type %d\n", opt);
	return 0;
}