std::string and contiguous memory?

[laserlight]

I argued that the implementation of a std::string is at the discretion of the compiler designers. Because of this, the internal memory of a std::string in not guaranteed to be contiguous, although, most probably do implement it that way. I went on to say that messing with its contents has undefined behavior.

You were right, however, since the 2011 edition of the C++ standard, the internal storage of the contents of a std::string is guaranteed to be contiguous:

The char-like objects in a basic_string object shall be stored contiguously. That is, for any basic_string object s, the identity &*(s.begin() + n) == &*s.begin() + n shall hold for all values of n such that 0 <= n < s.size().

That said, instead of calling data() and then casting away const-ness, I think that it would be better to use the &str[0] idiom (like how it is for std::vector), after checking that the string is not empty.

He then went on to say that I was “assuming” that the implementation of taking the address of the first element of a vector is well defined. Well, isn't it?

Yes, that has been guaranteed since the 2003 edition of the C++ standard.