Fortran compilers typically have options for enforcing Fortran standards.
The compilers raise additional warnings or errors for code that is not deemed compliant.
Fortran standard options can make false warnings, so we generally do not enable standards checking for user defaults.
However, we do enforce implicit none as a quality measure.
It’s also important to use implicit none so that each variable must be assigned beforehand.
We recommend the Fortran 2018 statement:
implicitnone(type,external)
which requires explicitly defined procedure interfaces as well.
type
the traditional implicit none default
external
new for Fortran 2018, requires explicit interface for external procedures.
Like other coding languages, Fortran code might have variables that are used before they are defined, or variables that are defined but never used.
Uninitialized variables cause unexpected behavior that can be difficult to debug.
Variables that are defined but never used are a waste of memory and possibly computation time and make the code less readable.
Here is a trivial example of a Fortran program that has an undefined variable, that Fortran compilers generally don’t warn about by default, and may not even be able to warn at compile time.
GCC / GFortran 17 adds two Fortran compiler options to provide more robust (less false positive and false negative) warnings about undefined and unused variables.
This is a potentially significant improvement over the
-Wuninitialized
and
-Wmaybe-uninitialized
flags, which operate on the
Static Single Assignment (SSA)
form and are known to be more likely to produce false positives and false negatives.
The LLVM Flang compiler has an option
-Wused-undefined-variable
that at least in Flang 22.1 didn’t catch the undefined variable in the toy example above, but does catch the unused variable with the option
-pedantic.
It is mentioned in the Flang forums that the Flang team considers some of the cases Gfortran 17 catches to be for possibly future implemented
runtime checks
rather than compile-time checks as in GCC 17.
warning: Value of uninitialized local variable ‘i’ is used but never defined [-Wused-undefined-variable]
The “nvfortran” compiler nvfortran -help didn’t reveal any options to detect undefined variables beyond the usual -Mdclchk that enforces implicit none - but that’s a declaration check, not a defined variable check.
Whether using Clang / LLVM or Homebrew GNU GCC compiler, GNU ld is not supported on macOS.
Only the Apple macOS
Xcode ld is supported.
The new
ld linker
in Xcode 15 broke numerous projects, including OpenMPI < 4.1.6.
Each of macOS, Windows, and Linux has a way to get and set which users have administrative privileges (i.e. can use sudo or are in the Administrators group) from Terminal.
On Windows, the users who are
Administrator
capable can be discovered from PowerShell using:
Get-LocalGroupMember -Group "Administrators"
Query a specific user to see if they are an Administrator:
$user = "myUsername"# put the desired username in the $user variable, then run the following command:Get-LocalGroupMember -Group "Administrators" | Where-Object { $_.Name -like "*\$user" }
Long-running Terminal programs might not be detected by the operating system on a laptop or other device that has power-saving sleep or suspend modes.
This can lead to disappointment as the long-running program hasn’t completed when the user checks back.
This
caffeinate Python script
works with:
To disable sleep while on AC power (charger), which is also suitable for fixed devices like a desktop, use
systemctl mask
to disable the sleep, suspend, hibernate, and hybrid-sleep targets:
For Windows, check and save to a text file the current power management settings with
powercfg:
powercfg /query
Look for “Current AC Power Setting Index” in the output for “Sleep” and “Hibernate” to see the current settings.
To disable sleep while on AC power (charger), which is also suitable for fixed devices like a desktop:
powercfg /change standby-timeout-ac 0
To set Hibernate to never while on AC power (charger), while allowing hibernate to be enabled for battery power (important for laptop tucked away for the weekend), run the following command:
powercfg /change hibernate-timeout-ac 0
Note that powercfg /hibernate off completely disables hibernate, which is not necessarily recommended for laptops that may be stored without power when not manually shut down each time.
While CMake binaries can be downloaded for most platforms, there are certain cases where one wishes to build CMake from source.
For example, when preparing a merge request to fix or enhance CMake.
Usually the computer will have at least an older version of CMake that can be used.
If so, we recommend using the existing CMake to build the newer CMake from the CMake source directory.
We recommend using
Ninja
in general for faster build and rebuild for any CMake project.
This puts the compiled CMake under ~/cmake-dev, without disturbing the primary CMake install.
Upon making any CMake code changes, simply recompile the minimum needed bits by:
Regardless of how an App is installed, whether through WinGet, the Microsoft Store, or a direct download, WinGet can be used to find the program install location on disk.
For example, to find the install location of the Microsoft Edge browser:
winget list msedge --details
(one can also use the names Microsoft.Edge or Edge)
The results include “Installed Location” which for this example may be examined like:
ls ${Env:ProgramFiles(x86)}/microsoft/edge/application
with results including the Edge executable msedge.exe.
Matlab external language
interfaces
includes .NET on Windows, Linux, and macOS.
This allows efficiently calling .NET assemblies and using .NET libraries directly from Matlab.
The Matlab function
dotnetenv
is used to set up and check the active .NET environment in Matlab.
Environment variable DOTNET_ROOT is vital for Matlab to detect the .NET installation, particularly on Linux and macOS.
If Matlab is having issues detecting the .NET installation NET.isNETSupported is false, determine the value for DOTNET_ROOT from system Terminal:
dotnet --info
If “dotnet” command is not found, install .NET SDK:
stop (1956 Fortran I): return integer on stderr (recommendation)
stop (Fortran 77): return integer or constant character, if character it may or may not be printed, but return code is 0 (no error)
error stop (Fortran 2008): constant character with error code
error stop (Fortran 2018): variable character with error code, also allowed inside pure procedure.
Fortran 2018 finally brought the needed behavior for convenient error messages and continuous integration.
CMake and Meson handle
automatic detection
of compiler supported features like error stop.
Fortran 2008 error stop with constant code:
Gfortran ≥ 5
NAG ≥ 6.0
Intel oneAPI
Nvidia HPC SDK
Fortran 2018 error stop with variable code
Gfortran ≥ 7
NAG ≥ 6.2
Intel oneAPI
Nvidia HPC SDK
Fortran 2018 error stop,QUIET=.true./.false.
NAG ≥ 6.2
This feature was promoted by Steve Lionel, but has not yet been widely adopted.
From the Fortran 2018 standard, 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.
Over time, 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.
stop1
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.
The Fortran 77 standard defines the character string as “accessible” but doesn’t define where it goes.
A best practice if desired to print a message when stopping a program is with explicit “print” or “write” statement.
stop with integer code is still normal program termination in modern Fortran.
Since Fortran 77, stop may instead return a constant scalar character like “goodbye”.
This generally sets 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 taking 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.
Fortran 2008 error stop with constant string or integer code: both return non-zero exit status on stderr.
use,intrinsic::iso_fortran_env,only:stderr=>error_unitwrite(stderr,*)'the failure was in '//failedmoderror 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.
Fortran 2018 error stop variable character string allows for cleaner syntax, for example: