C++ helpers: s_set_id generates the same id if called on the same host

[luca-drf]

In the definition of s_set_id (zmq::socket_t &) in zhelpers.hpp the random function (in within macro) is not seeded, hence, if called from the same host generates always the same id.

So the following code if called from different processes (or threads) on the same host prints always the same id:

#include "zhelpers.hpp"

int main(){
    zmq::context_t context(1);
    zmq::socket_t client(context, ZMQ_REQ);

    std::cout << s_set_id(client) << std::endl;
    return 0;
}

Suggested fix: add srand(time(NULL)) at the beginning of s_set_id (zmq::socket_t &) body in C++/examples/zhelpers.hpp

[myd7349]

@radome
You should call srand only once in your program. Please refer this question on stackoverflow: Same random numbers every loop iteration.

For the same reason, we can not put the call to srand in s_set_id(Someone may call s_set_id from multiple threads or in a for loop). Instead, we should call srand ourselves at the beginning of the program. Just like most of the examples do(rtdealer.c#L59, for instance).

You may refactor your code like this:

#include "zhelpers.hpp"

int main(){
    zmq::context_t context(1);
    zmq::socket_t client(context, ZMQ_REQ);

    srandom((unsigned)random(NULL));

    std::cout << s_set_id(client) << std::endl;
    return 0;
}