Question

So what are main differences and which of them will be used in which cases?

Answer 1

• vector<char> gives you a guarantee that &v[0]+n == &v[n] whereas a string doesn’t (practically, it is the case, but there is no guarantee)… AFAIK C++0x gives that guarantee already
• there is no implicit conversion from const char* to vector<char>
• string is not an STL container. For example, it has no pop_back() or back() functions
• And last, but not least, different member functions! String gives you functions suitable for strings, like returnig a null-terminated string with c_str()

Bottom line: Use string when you need to operate with strings. Use vector<char> when you need a … well, vector of individual chars…

Another use of vector<char> is a way to avoid vector<bool> specialization.