stop(1956 Fortran I): return integer on stderr (recommendation)
stop(Fortran 77): return integer or constant
character– no integer return with character
error stop(Fortran 2008): constant character with error code
error stop(Fortran 2018): variable character with error code, also allowed inside
Fortran 2018 finally brought the needed behavior for convenient error messages and continuous integration.
CMake and Meson handle
of compiler supported features like
error stop with constant code:
- Gfortran ≥ 5
- NAG ≥ 6.0
- Intel oneAPI
- Nvidia HPC SDK
error stop with variable code
- Gfortran ≥ 7
- NAG ≥ 6.2
- Intel oneAPI
- Nvidia HPC SDK
This feature was promoted by Steve Lionel, but has not yet been widely adopted.
My understanding of the Fortran 2018 standard is that the
quiet= parameter not only suppresses any console output but also may suppress the error code?
I would prefer to have the error return code, without the console text.
Since Fortran I in 1956, the
stop statement has generally displayed a return code to indicate an error if an integer value was provided.
stop statement behavior has changed to allow more refined signaling on program stop.
Since Fortran I in 1956,
stop without return code to stop execution normally has been supported, along with
stop with integer return code to indicate abnormal termination.
The Fortran 2008 and 2018 standards recommend that the error code be returned on
iso_fortran_env: error_unit, which was first defined in Fortran 2003 standard.
Earlier standards don’t say where the error code should go.
Through Fortran 2018,
stop with integer code is still normal program termination.
Since Fortran 77,
stop may instead return a constant scalar character like “goodbye”.
This generally sets stderr return code to 0, that is, no error is indicated.
For continuous integration, having a reliable way to indicate error behavior is crucial. For HPC, indicating abnormal conditions to the shell is also vital to avoid wasted resources on runs that suffered a computational error.
Fortran 2008 brought the long overdue
error stop statement.
stop still indicates normal program termination, and can for example stop individual images in a parallel executing program.
Say an individual cell in a 3-D simulation did not find a stable solution.
Depending on the simulation, that can be OK, perhaps set that value to NaN and
stop with an error code on stderr, while letting the other images continue running.
However, in other types of simulations, an early failure to converge to a solution in a cell may invalidate the entire simulation taking a month of CPU time.
Instead of writing cumbersome external checking code, the programmer can instead use
error stop to reliably terminate all images when a critical failure is detected.
error stop with constant string or integer code: both return non-zero exit status on stderr.
use, intrinsic:: iso_fortran_env, only: stderr=>error_unit write(stderr,*) 'the failure was in ' // failedmod error stop
Fortran 2018 added
error stop with variable scalar string or variable integer code.
A vital addition of Fortran 2018 is that
error stop can be used within
pure procedures, a very commonly needed use case.
error stop variable character string allows for cleaner syntax, for example:
error stop 'the failure was in ' // failedmod