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c++macosdynamic-library

dlsym() usage fails for rand

I'm trying to call rand using dlfcn.h (d.

I have this code, based on a project I'm working on. The core issue for me is that when used this way, it compiles and even runs, but its output is

cif: cif is OK
rand val: 16807

And the value of rand val is 16807 every time, contrary to what rand is supposed to do. What am I doing wrong here?

Solution

  • You only call rand() once. If unseeded, rand() is probably going to use a static seed, probably zero (library-dependent).

    Import srand too, and seed it with a reasonably random quantity - for example, you could do

    timeval tv;
gettimeofday(&tv, NULL);
srand_ptr(tv.tv_sec ^ tv.tv_usec);

    to seed it with the current time (seconds and microseconds).

    Alternatively, on OS X, consider using arc4random instead, which is automatically seeded and generally produces better random numbers.