CZMQ set send HWM / set receive HWM

Question

Doesn't this have to work?

#include <czmq.h>

zsock_t *sockout = zsock_new_pub("inproc://a");
zsock_set_sndhwm (sockout, 20);

How to set HWM and/or BUF sizes?

UPDATE: I added some more code and works in this context:

#include <string>
#include <czmq.h>

int main (void){

    zsock_t *sockout = zsock_new_pub("inproc://a");
    zsock_set_sndhwm (sockout, 20);
    std::string data2send;
    for (size_t i = 0; i < 1000; i++){
        data2send = "data" + std::to_string(i);
        zsock_send(sockout, "s", data2send.c_str() );
    }
}

Although zsock_set_sndhwm (sockout, 20); works in this particular context. I have to figure out the context where it doesn't works.

Answer 1

I am answering my own question for a complete solution pub/rec

Publisher code:

#include <string>
#include <czmq.h>

int main (void)
{
    zsock_t *sockout = zsock_new_pub("ipc://a");
    zsock_set_sndhwm (sockout, 20);
    zsock_set_rcvhwm (sockout, 20);

    std::string data2send;
    for (size_t i = 0; i < 1000; i++){
        data2send = "data: " + std::to_string(i);
        sleep(1);
        zsock_send(sockout, "s", data2send.c_str() );
    }
}

Subscriber (Receiver) code:

#include <string>
#include <czmq.h>
#include <iostream>

int main (void){
    zsock_t *sockin = zsock_new_sub("ipc://a", "");
    zsock_set_sndhwm (sockin, 20);
    zsock_set_rcvhwm (sockin, 20);

    char *m;
    std::string m_str;

    while(true){
        zsock_recv(sockin, "s", &m);
        std::cout << "**READ: " << m << "\n\n";
    }
}