Does fgets() always null-terminate the string it returns?

Question

Is this safe to do? Does fgets terminate the buffer with null or should I be setting the 20th byte to null after the call to fgets and before I call

Answer 1

Yes fgets() always properly null-terminates the buffer. From the man page:

The fgets() function reads at most one less than the number of characters specified by n from the given stream and stores them in the string s. Reading stops when a newline character is found, at end-of-file or error. The newline, if any, is retained. If any characters are read and there is no error, a '\0' character is appended to end the string.