C++ The complexity of string concatenation in C++ and Java

[Hilton D]

Consider the following code:

public String joinWords(String[] words) {
    String sentence = "";
    for(String w : words) {
        sentence = sentence + w;
    }
    return sentence;
}

Because each concatenation generates a new copy of the string, the overall complexity is O(n2). Fortunately, in Java, we could handle this using a StringBuffer, which has O(1) difficulty for each add, resulting in the overall complexity of O. (n).

In C++, std::string::append() has an O(n) complexity, and I'm not sure what the complexity of stringstream is.

Are there methods in C++ that are as sophisticated as those in StringBuffer?

StringBuilder Class in Java