Is std::string inferior to QString?

Question

A colleague of mine claims that the implementation and especially the memory management of std::string is inferior to that of the QString in the Qt library. What aspects of the std::string could this refer too?

Answer 1

Regarding memory management, QString uses copy-on-write, which is now explicitly forbidden in the C++ standard library. But there is a reason for that. The copy-on-write idiom performs worse in multi-threaded environment as it requires synchronization. This article discusses the problems in more details.

Implementations of std::string on the other hand typically use small-string-optimization (SSO) to avoid any dynamic memory allocation for small strings. That is the current state of the art for strings.

Answer 2

With the memory management, you'll have to decide what is better for your application. But one place where QString clearly shines in contrast to std::string, is the unicode support. QString stores an UTF-16 encoded string internally, while std::string is encoding agnostic. This often makes it much simpler to use QString rather then std::string when you have to deal with user-supplied multi-byte encoded strings.