Is read-only access to a vector (vector::operator[] and vector::size()) asynchronous-safe?

Question

My program needs to perform read-only access to the contents of a vector<string> in a signal handler for SIGINT. (The alternative is to use a fixed-size array of fixed-length C strings.) The program is designed to run in a POSIX environment.

Are vector::operator[] and vector::size() asynchronous-safe (or signal-safe)?

Answer 1

No, it's not safe. C++11 1.9/6:

When the processing of the abstract machine is interrupted by receipt of a signal, the values of objects which are neither

• of type volatile std::sig_atomic_t nor
• lock-free atomic objects (29.4)

are unspecified during the execution of the signal handler, and the value of any object not in either of these two categories that is modified by the handler becomes undefined.