Question

Is it valid (defined behavior) to access a string literal simultaneously with multiple threads? Given a function like this:

const char* give()
{
  return "Hello, World!";
}

Would it be save to call the function and dereference the pointer simultaneously?

Edit: Many answers. Will accept the first one who can show me the section out of the standard.

Answer 1

According to the standard:

C++11 1.10/3: The value of an object visible to a thread T at a particular point is the initial value of the object, a value assigned to the object by T, or a value assigned to the object by another thread, according to the rules below.

A string literal, like any other constant object, cannot legally be assigned to; it has static storage duration, and so is initialised before the program starts; therefore, all threads will see its initial value at all times.

Older standards had nothing to say about threads; so if your compiler doesn’t support the C++11 threading model then you’ll have to consult its documentation for any thread-safety guarantees. However, it’s hard to imagine any implementation under which access to immutable objects were not thread-safe.