language agnostic - what is the difference between re-entrant function and recursive function in C?

Question

In C I know about the recursive function but I heard about the re-entrant function.

What is that? And whats the difference between them?

Answer 1

It's easier to remember when you understand what the term means.

The term "re-entrant" means that it is safe to "re-enter" the function while it is already executed, typically in a concurrent environment.

In other words, when two tasks can execute the function at the same time without interfering with each other, then the function is re-entrant. A function is not re-entrant when the execution by one task has an impact on the influence of another task. This typically is the case when a global state or data is used. A function that uses only local variables and arguments is typically re-entrant.