Question

while doing some TMP 🙂 🙁
I ended up needing the size of the element that STL container holds.
I know that usually deref an container.begin() iterator is bad without checking if container isnt empty, but from what I know sizeof is compiletime macro so I guess it is safe.
Am I right?

code snippet is :

    for(auto it = t.begin(); it!= t.end(); ++it)
    {
        char* cp = (char*)(&(*it));
        for (size_t i =0 ; i < sizeof *t.begin();++i)
        //...
    }

Answer 1

Yes, that’s safe, but realize that you can get at the types stored in a container via the key_type, mapped_type and/or value_type typedef members.

E.g.:

struct Foo {
    int bla;
    double quuxly;
};

int main()
{
    typedef std::vector<Foo> foovector;
    std::cout << "sizeof(Foo) == " << sizeof(foovector::value_type) << "\n";
}

[sizeof is not a macro, btw. It’s an operator built into the language itself, like ++ or |=.]