Stop with non-zero exit status

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Searching for this question I found this SO thread, and the suggestion is to use stop N. Is that a standard way to do it? Seems from the discussion that sometimes the number gets printed, or not, depending on the OS or the compiler.

What I want is a flag to allow easier handling of errors from the output of a Fortran program, using an upper level script.

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The Fortran 2018 standard says:

If the stop-code is an integer, it is recommended that the value be used as the process exit status, if the processor supports that concept.

If QUIET= is omitted or the scalar-logical-expr has the value false:
• …
• if a stop code is specified, it is recommended that it be made available by formatted output to the same unit.

(ERROR_UNIT, I think)

Note there is also the ERROR STOP statement:

Execution of a STOP statement initiates normal termination of execution. Execution of an ERROR STOP statement initiates error termination of execution.

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A process exit code has not always been a thing, and thus the Fortran standard cannot mandate anything about it. I will note that I have had fairly good luck with stop n passing n as the exit code on all platforms and compilers that I care about. I will note that detecting it on Windows is occasionally a bit finicky, I suspect more due to the idiosyncrasies of the cmd and/or batch shells than problems in the Fortran compilers or run-time systems.

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When using stop 1 (for example), this becomes output on the program termination, like:

ERROR: Invalid input parameter.
STOP 1

Is it possible to suppress that printing?

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STOP 1, QUIET=.TRUE.

is the Standard’s way

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That is perfect, thank you!

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By the way, that blog has many interesting short and recent articles in the Fortran category:

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I have also been using stop 1, that seemed to work everywhere. Recently I switched to error stop.

Regarding the quiet part, with GFortran 11.0.1 I get:

$ gfortran a.f90
a.f90:1:7:

    1 | STOP 1, QUIET=.TRUE.
      |       1
Error: Syntax error in STOP statement at (1)

So I don’t know if I am doing anything wrong.

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It seems that it is feature not implemented yet?

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84519

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Looks like GFortran’s parser cannot parse it yet. In LFortran we can parse it:

$ cat b.f90 
program test
STOP 1, QUIET=.TRUE.
end
$ lfortran --show-ast b.f90 
(TranslationUnit [(Program test () [] [] [] [(Stop 0 1 (Logical .true.) ())] [])])

But the quiet=.true. gets lost by the time it gets to ASR:

$ lfortran --show-asr b.f90
(TranslationUnit (SymbolTable 1 {test: (Program (SymbolTable 2 {}) test [] [(Stop (ConstantInteger 1 (Integer 4 [])))])}) [])

And by the time it gets to LLVM, also the non-zero exit code gets lost:

$ lfortran --show-llvm b.f90
; ModuleID = 'LFortran'
source_filename = "LFortran"

@0 = private unnamed_addr constant [6 x i8] c"STOP\0A\00", align 1

define i32 @main() {
.entry:
  call void (i8*, ...) @_lfortran_printf(i8* getelementptr inbounds ([6 x i8], [6 x i8]* @0, i32 0, i32 0))
  call void @exit(i32 0)
  ret i32 0
}

declare void @_lfortran_printf(i8*, ...)

declare void @exit(i32)

We need to fix it: Implement nonzero exit code and `quiet` in STOP (#597) · Issues · lfortran / lfortran · GitLab

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