Never throw while being the direct owner of an object

Reason

That would be a leak.

Example

void leak(int x)   // don't: might leak
{
    auto p = new int{7};
    if (x < 0) throw Get_me_out_of_here{};  // might leak *p
    // ...
    delete p;   // we might never get here
}

One way of avoiding such problems is to use resource handles consistently:

void no_leak(int x)
{
    auto p = make_unique<int>(7);
    if (x < 0) throw Get_me_out_of_here{};  // will delete *p if necessary
    // ...
    // no need for delete p
}

Another solution (often better) would be to use a local variable to eliminate explicit use of pointers:

void no_leak_simplified(int x)
{
    vector<int> v(7);
    // ...
}

Note

If you have a local "thing" that requires cleanup, but is not represented by an object with a destructor, such cleanup must also be done before a throw. Sometimes, finally() can make such unsystematic cleanup a bit more manageable.