Is this a reliable way of generating a GUID?

Question

I'm trying to generate a GUID in a platform agnostic manner, most search results suggest using BOOST or platform specific libraries. I remember once coming across the following snippet and I was wondering if this is a reliable way of generating GUID's:

unsigned int generateGuid()
{
    char c;
    return (unsigned int)&c;
}

More specifically, does this guarantee a unique value always? And if not, what are some good lightweight and cross-platform approaches of doing this?

Answer 1

A basic example:

#include <boost/uuid/uuid.hpp>            // uuid class
#include <boost/uuid/uuid_generators.hpp> // generators
#include <boost/uuid/uuid_io.hpp>         // streaming operators etc.

int main() {
    boost::uuids::uuid uuid = boost::uuids::random_generator()();
    std::cout << uuid << std::endl;
}
Example output:

Answer 2

No it is not. This function will return some address from stack depending on where it is called. In two subsequent calls or tight loop it will be always the same address. For example in Visual Studio the default stack size is 1 MB, I think, so in the best case you will get one million unique values. Typical program does not use more than 1KB of stack so in that case you will get at most one thousand unique values.