Scientific Computing

Install Gfortran or Flang compiler on macOS Homebrew

Homebrew can install Fortran compilers including GCC and LLVM Flang.

Gfortran

Gfortran comes with GCC Homebrew package:

brew install gcc

As a complete C / C++ / Fortran compiler package, Gfortran doesn’t require additional flags or environment variables.

LLVM Flang

LLVM Flang is currently a separate package from the LLVM C/C++ compilers:

brew install flang

Currently, Flang from Homebrew may require additional flags or environment variables:

export LIBRARY_PATH=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib
# where libSystem.tbd and libc++.tbd are

additionally, it may be necessary to specify the path to the C++ standard library:

export LDFLAGS=-lc++

on the command line, this can look like:

flang-new main.f90 -L/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/lib -lc++

Iterate Matlab versions with CMake

These techniques work with any versioned program or library. Here we use Matlab as an example. CMake find_package with a version range would be used to simply select from a known-working version range.

Many Matlab codes require a modern version of Matlab. It’s possible to select from an arbitrary min…max range of Matlab versions with CMake FindMatlab as follows. This technique works with other versioned programs and libraries as well.

foreach(v IN ITEMS 23.2 24.1 24.2)
  find_package(Matlab ${v} EXACT COMPONENTS MAIN_PROGRAM)
  if(Matlab_FOUND)
    add_test(NAME matlab-${v}
      COMMAND ${Matlab_MAIN_PROGRAM} -batch "buildtool"
      WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
      )
  endif()
endforeach()

Git SSL certificate location

Git typically works for HTTPS URLs using the default configuration. If certificates are not working, try configuring Git with the system SSL certificate location.

git config --global http.sslCAInfo /path/to/cert.crt

Git environment variable “GIT_SSL_CAINFO” can override this. This can be used to override missing or incorrect SSL certificate locations for Git operations in programs like Matlab.

To disable SSL certificate verification, set environment variable “GIT_SSL_NO_VERIFY” to “1”, but be aware of the security implications e.g. MITM.

Free C C++ Fortran compiler families

Several modern, currently-supported compiler families are free-to-use for C, C++ and Fortran.

GCC has broad support of modern standards on a very wide range of computing platforms. GCC’s downside in some cases can be slower runtime performance than compilers having less broad language and platform support.

Compiler C C++ Fortran
GNU gcc: C23 g++ C++26 gfortran: F2018
Intel oneAPI icx: C23 icpx: C++23 ifx: F2023
LLVM clang: C17 clang++: C++26 flang-f18: F2018
AOCC clang: C17 clang++: C++17 flang: F2008
NVIDIA HPC SDK nvc: C11 nvc++: C++23 nvfortran: F2003
IBM OpenXL xlc: C17 xlc++: C++26 xlf: F2018

Intel oneAPI compilers are free to use for any user. The Intel performance libraries like MKL, IPP, and TBB are available at no cost.


LLVM Clang and Flang have significant industry support, including from Nvidia, and are known for high performance.


AMD AOCC LLVM compiler is tuned for AMD CPUs.


NVIDIA HPC SDK is free to use. A key feature of the HPC SDK compilers is intrinsic support for CUDA Fortran.


IBM OpenXL LLVM-based compilers are currently for POWER CPUs only e.g. ppc64le. IBM OpenXL compilers do not work with a typical x86-based computer.

CMake macOS Xcode Environment

Related: GCC / Clang header clash on macOS


When macOS, Xcode, or Command Line Tools upgrades, build directories (including for CMake-based projects) often need to be refreshed. If the user has set custom environment variables concerning Xcode, they may need to be updated as well. Here are some important environment variables and CMake variables to check if problems occur after upgrading.

For a simple CMake project on macOS, CMakeCache.txt might include:

CMAKE_OSX_DEPLOYMENT_TARGET:STRING=

CMAKE_OSX_SYSROOT:PATH=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX*.sdk

Having multiple directories under the following is fine:

  • /Library/Developer/CommandLineTools/SDKs
  • /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs

CMake can select the appropriate SDK by the user specifying environment variable SDKROOT or by selecting the SDK:

xcode-select --switch

The XCode versions that Homebrew targets can be found in xcode.rb.

Workarounds

If Homebrew GCC breaks after upgrading Xcode or Command Line Tools, try specifying an older SDK. For example, if g++-14 main.cpp -v shows a different (older) SDK than CMake and it works, try specifying that SDK in environment variable SDKROOT. Note that the SDK version corresponds to macOS version, not the XCode version. For example, if the latest SDK is MacOSX14.4.sdk, try using MacOSX13.3.sdk in “~/gcc.sh”:

export CC=gcc-14 CXX=g++-14 FC=gfortran-14

export SDKROOT=/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/

and then source ~/gcc.sh before running cmake with a fresh build directory.

If a CMake build step fails, try copy-pasting the command and removing the -isysroot portion of the command. This is a clear clue the older SDK is (at least temporarily) needed till Homebrew updates its GCC formula.

GCC will tell where included files are coming from by adding the gcc -H flag. This tells what to specify for environment variable SDKROOT.

Example minimal project

Zoom audio toggle indicator

As per the Release Notes:

The Zoom app offers an option to play audio tones when muting or unmuting the microphone, providing enhanced accessibility for users with visual impairments or other disabilities. This setting is OFF by default and can be enabled from the Zoom Workplace app under Settings then Audio. When enabled, users will hear a tone, audible only to them, indicating the mute or unmute action.

CMake variables in SCRIPT role

When running CMake standalone scripts like cmake -P script.cmake this is the SCRIPT CMake role. Not all CMake information variables are set in SCRIPT role, in particular, the CMAKE_HOST* and CMAKE_SYSTEM* variables are not set as they are in PROJECT role.

This is a workaround for cmake -P SCRIPT role to get the CMAKE_HOST_* variables. It uses undocumented CMake-internal scripts, but they’ve been present since 2012 and may be unlikely to change.

message(STATUS "CMake ${CMAKE_VERSION}")

get_property(cmake_role GLOBAL PROPERTY CMAKE_ROLE)
if(cmake_role STREQUAL "SCRIPT")
  set(CMAKE_PLATFORM_INFO_DIR ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY})
  # define CMAKE_HOST*, CMAKE_SYSTEM*, etc.
  include(${CMAKE_ROOT}/Modules/CMakeDetermineSystem.cmake)
  # set booleans like CYGWIN
  include(${CMAKE_ROOT}/Modules/CMakeSystemSpecificInitialize.cmake)

  # needed by Modules/Platform/*.cmake
  include(${CMAKE_ROOT}/Modules/CMakeSystemSpecificInformation.cmake)

  # define CMAKE_SHARED_LIBRARY_SUFFIX, CMAKE_SHARED_LIBRARY_PREFIX, etc.
  include(${CMAKE_ROOT}/Modules/Platform/${CMAKE_SYSTEM_NAME}.cmake)
endif()

message(STATUS "CMAKE_SYSTEM:                ${CMAKE_SYSTEM}")
message(STATUS "CMAKE_SYSTEM_NAME:           ${CMAKE_SYSTEM_NAME}")
message(STATUS "CMAKE_SYSTEM_VERSION:        ${CMAKE_SYSTEM_VERSION}")
message(STATUS "CMAKE_SYSTEM_PROCESSOR:      ${CMAKE_SYSTEM_PROCESSOR}")
message(STATUS "CMAKE_HOST_SYSTEM:           ${CMAKE_HOST_SYSTEM}")
message(STATUS "CMAKE_HOST_SYSTEM_NAME:      ${CMAKE_HOST_SYSTEM_NAME}")
message(STATUS "CMAKE_HOST_SYSTEM_VERSION:   ${CMAKE_HOST_SYSTEM_VERSION}")
message(STATUS "CMAKE_HOST_SYSTEM_PROCESSOR: ${CMAKE_HOST_SYSTEM_PROCESSOR}")
message(STATUS "CMAKE_SHARED_LIBRARY_SUFFIX: ${CMAKE_SHARED_LIBRARY_SUFFIX}")
message(STATUS "CMAKE_SHARED_LIBRARY_PREFIX: ${CMAKE_SHARED_LIBRARY_PREFIX}")
message(STATUS "CMAKE_STATIC_LIBRARY_SUFFIX: ${CMAKE_STATIC_LIBRARY_SUFFIX}")
message(STATUS "CMAKE_STATIC_LIBRARY_PREFIX: ${CMAKE_STATIC_LIBRARY_PREFIX}")

Meson C++ standard with fallback

Meson can set a default C++ (or C) langauge standard level with fallback to older versions. This allows recent compilers to support the full functionality of the project code, while falling back for older compilers.

get_option('cpp_std') can be used for logic within meson.build if desired.

project('ffilesystem', ['cpp'],
default_options: ['c_std=c99', 'cpp_std=c++23,c++20,c++17', 'buildtype=release', 'b_ndebug=if-release'])

cpp_std = get_option('cpp_std')

message('C++ standard: ' + cpp_std)

The C / C++ code can use macro feature checks that detect compiler C++ / C standard support.

#if __cplusplus >= 201703L
// C++17 features
#endif

For C code likewise:

#if __STDC_VERSION__ >= 201112L
// C11 features
#endif

Related: CMake C++ standard with fallback

C feature macros that stdlib.h may need

When reading the documentation for a C library function, you may see a note that the function requires a feature test macro to be defined. This is common for functions that are not part of the C standard library but are part of POSIX or another standard. The feature test macro tells the compiler to include the necessary headers and definitions for the function.

Often the “_DEFAULT_SOURCE” macro is sufficient. Try doing in C like:

#if defined(__linux__) && !defined(_DEFAULT_SOURCE)
#define _DEFAULT_SOURCE
#endif

Switch CMake Generator to Ninja

The default CMake build generator is operating system dependent. In general many projects can benefit from increased build speed and especially rebuild speed of Ninja. Switch the default build generator on any platform by setting environment variable CMAKE_GENERATOR.

CMAKE_GENERATOR=Ninja

Ninja executable can be installed by any one of:

  • download
  • WinGet: winget install Ninja-build.Ninja
  • Python: pip install ninja
  • Homebrew: brew install ninja
  • Alpine Linux: apk add ninja-build

Add the location of the Ninja executable to environment variable $PATH or CMAKE_PROGRAM_PATH.


Note that Ninja work-alikes like Samurai “samu” might get installed by default by some package managers. These work-alikes might not have a new-enough Ninja API equivalent, so in those cases install the actual Ninja program.


If using Conan Package Manager, tell Conan to use Ninja by setting environment variable

CONAN_CMAKE_GENERATOR=Ninja