Is the: "std::string can hold '\0' character" by design?

Question

The fact that std::string can actually hold '\0' characters comes up all the time. This is of course inconsistent with C-style strings.

So I'm wondering, is this by design, or is it an omission, or is it just the fact that standard doesn't forbid it and compilers allow this to happen?

Answer 1

I'm wondering what your quarrel is. '\0' is just another character. There is no efficient way to forbid it in a general purpose 'char' string. That the same character has a special meaning in C is unfortunate but has to be dealt with as every restriction that is imposed by legacy code as soon as you interoperate with it.

This shouldn't be an issue as long as you stick to code that uses std::string exclusively.

To address your comment we need to look at the constructor that takes a char* which would be basic_string(const charT* s, const Allocator& a = Allocator()) in 21.4.2 9/10 in n3242. It says that the size of the internal string is determined through traits::length(s) which in the case of std::string is strlen which requires its argument to be null terminated. So yes, if you try to construct a std::string from an const char* it needs to be null terminated.

Answer 2

There is a set of functions that accept 'char *' arguments and assume that the string is terminated by a zero. If you use them carefully, you can certainly have strings with 0's in them.

STL strings, in contrast, intentionally permit zero bytes, since they don't use 0 for termination. So the simple answer to your question is, 'yes, by design.'