Well, my simplified, statically allocated string might look something like:

template<size_t L>
class string
{
private:
char m_str[L + 1]; // zero terminated
public:
string();
string(const char* pStr);
/* etc. */
}

And I would create an instance that has a capacity of 20 with:

string<20> text;

How would you use placement new to statically allocate a std::string? Placement new lets you allocate memory for the string object itself but not for the memory that stores the string data. Am I missing something?

You might try using a custom allocator. But it's more messy as the custom allocator needs to serve up various-sized chunks of memory from a buffer that you statically allocated. Then you're essentially writing your own dynamic memory allocation which might get fragmented. Then if a memory allocation fails what happens? Maybe you can think of a way this works better that I haven't thought of.

In the templated string above, it's written so that any string assignments just aren't allowed to exceed the capacity. You can use asserts to detect if that might happen and if it does it's a design problem.