strtok function thread safety

strtok() is not MT-safe because it stores some intermediate variables globally and reuse them at each call (see you don't have to pass again the string each time you call strtok()). You can have a look at the man pages of methods you are using and it is always indicated at the end if it is MT-safe or not.

When a method is not MT-safe (multi-thread safe or reentrant), you should look for same method with suffix _r meaning reentrand. In your example, strtok_r() as suggested in the other answer.

strtok() is not reentrant so it should not be used from threaded applications, use strtok_r() instead.