In Chapter 1, Getting Started, and Chapter 2, Introduction to Sockets, we worked on programs with a single socket. Working on one socket is easy, but working on multiple sockets is somewhat tricky. To work with multiple sockets, we use zmq_poll(3), which is an event loop that allows an application to multiplex I/O with multiple sockets.
/*
Polling with ZeroMQ
*/
#include <string.h>
#include "zmq.h"
int main (int argc, char const *argv[]) {
void* ctx = zmq_ctx_new();
void* pull = zmq_socket(ctx, ZMQ_PULL);
zmq_connect(pull, "tcp://localhost:4040");
void* subscriber = zmq_socket(ctx, ZMQ_SUB);
char* company_name = "Company1";
int length = strlen(company_name) + 1;
zmq_connect(subscriber, "tcp://localhost:5050");
zmq_setsockopt(subscriber, ZMQ_SUBSCRIBE, company_name, length);
printf("starting...\n");
zmq_pollitem_t polls[2];
polls[0].socket = pull;
polls[0].fd = 0;
polls[0].events = ZMQ_POLLIN;
polls[0]...