How to cleanse (overwrite with random bytes) std::string internal buffer?

Consider a scenario, where std::string is used to store a secret. Once it is consumed and is no longer needed, it would be good to cleanse it - overwrite the memory that contained it, thus hiding the secret.

std::string provides a function const char* data() returning a pointer to (since C++11) continous memory.

Now, since the memory is continous and the variable will be destroyed right after the cleanse due to scope end, would it be safe to:

char* modifiable = const_char<char*>(secretString.data());
OpenSSL_cleanse(modifiable, secretString.size());

According to standard quoted here:

$5.2.11/7 - Note: Depending on the type of the object, a write operation through the pointer, lvalue or pointer to data member resulting from a const_cast that casts away a const-qualifier68) may produce undefined behavior (7.1.5.1).

That would advise otherwise, but do the conditions above (continous, to-be-just-removed) make it safe?