Scientific Computing

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 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.

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.

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.

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

• environment variable MACOSX_DEPLOYMENT_TARGET helps set CMAKE_OSX_DEPLOYMENT_TARGET
• Environment variable SDKROOT helps set CMAKE_OSX_SYSROOT

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

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.

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 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

We usually avoid the WSL default of putting the full Windows PATH into WSL. Particularly when using a build system like CMake, there will be Windows libraries that WSL-based CMake thinks it can use that it actually can’t.

Fix by editing Windows file $HOME/.wslconfig inside the WSL distro:

[interop]
enabled=false
appendWindowsPath=false

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

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