Return value of strerror(errno) when errno is out of range?

[Charan]

What would be the return value of strerror(errno) when errno is out of range.

say strerror(2022).

How shall I check this in a if condition?

[Dennis Handly]

strerror(3) says it returns a pointer to a NULL string:

   const char *p = strerror(2022).

   if (p[0] == '\0') {

      // Not a valid errno

   }