unchecked-stat (C181)

This rule is turned on by default.

What does it do?

This rule detects whether a stat, iostat, and cmdstat argument is checked within the same scope it is set.

Why is this bad?

By default, allocate statements will abort the program if the allocation fails. This is often the desired behaviour, but to provide for cases in which the developer wants to handle allocation errors gracefully, they may optionally check the status of an allocate statement by passing a variable to the stat argument:

allocate (x(BIG_INT), stat=status)
if (status /= 0) then
  call handle_error(status)
end if

However, if the stat variable is not checked, the program will continue to run despite the allocation failure, which can lead to undefined behaviour. Similar behaviour is exhibited by deallocate and IO statements such as open, read, and close.

To avoid confusing and bug-prone control flow, the checks on status parameters should occur within the same scope in which they are set.