CZMQ set send HWM / set receive HWM - c++

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";
}
}