Determine free space on Linux / macOS / Windows Subsystem for Linux with "
ncdu.
ncdu uses Ncurses terminal graphics to quickly show the biggest files in the Linux filesystem tree.
ncdu is very handy to find large files or directories that may be unneeded.
df -h
gives a drive-level summary of disk usage.
Package managers cache installed files in case of need to reinstall, but the packages can be redownloaded if needed to save disk space by clearing the cache.
Clear the package cache–for
APT
(common in Debian-based systems):
TeX Live documentation can consume a lot of disk space.
To cleanup the documentation, consider removing packages matching texlive-*doc.
This also removes texlive-full but with no detriment to TeX Live working.
Packages removed for texlive-doc to save over 1 GB of disk space.
For all CMake find_*() commands including
FindOpenSSL,
the package path can be hinted by setting an appropriate environment variable or CMake variable.
This examples supposes a Homebrew package manager has installed OpenSSL, which the user wishes to use in a CMake project.
To hint the package path when configuring a CMake project, either specify OpenSSL_ROOT by environment variable:
Homebrew uses subdirectories to separate different versions of packages.
CMake does not recursively search as that would in general not have a stopping condition and at least significantly slow down the search performance.
GitHub Actions macOS
runners use Apple Silicon CPU,
which is what most Apple users have.
Some build issues including the linker have historically had Apple Silicon-specific issues.
Generally it’s good to test on the same CPU architecture as the target platform.
We sometimes find it necessary to
select
the
Xcode version
compatible with
Homebrew GCC
if build errors occur that are not present on a physical Apple Silicon laptop.
The undocumented, discontinued macOS command-line utility
airport–
not to be confused with the Airport Utility app–gave detailed information about the current WiFi connection and nearby WiFi APs.
This utility was located at /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport.
Since discontining airport, current BSSID requires using CoreWLAN framework as demonstrated in Python
scan-wifi-python.
PowerShell tilde expansion was dropped in 7.4.0.
Automatic variable $home
remains available across operating systems.
ls $home
PowerShell
tilde expansion
was fraught with
difficulties
that led PowerShell maintainers to at least temporarily drop tilde expansion in PowerShell 7.4.0.
Note that automatic variables are just inside PowerShell itself–they are not environment variables.
Thus, automatic PowerShell variables are generally not visible to other programs or scripts unless additional steps are taken to expose them, perhaps as a command line argument or environment variable.
Aspell creates backup files with a .bak extension by default.
To turn off the backup files configure Aspell to not create them.
Often there is not a not a
user configuration file
“aspell.conf” present.
Even if there is a config file present, it can be overridden by environment variable ASPELL_CONF:
Unix-like HPC systems often have shared temporary scratch directories mapped by environment variable $TMPDIR to a directory like “/scratch” or “/tmp”.
$TMPDIR may be used for temporary files during build or computation.
$TMPDIR is often shared among all users with no expectation of preservation or backup.
If user files are left in $TMPDIR, the HPC system may email a periodic alert to the user.
If the user determines that $TMPDIR files aren’t needed after the HPC batch job completes, one can clear $TMPDIR files with a command near the end of the batch job script.
Carefully consider whether this is appropriate for the specific use case, as the scratch files will be permanently deleted.
rm -r -i $TMPDIR 2>/dev/null
Verify that deletes only the user’s files, as each user’s files have write permissions only for their own files.
Once this is established, to use this command in batch scripts replace the “-i” with “-f” to make it non-interactive.
Building Windows shared libraries in general creates DLLs whose directory must be on environment variable PATH when the executable target is run.
Windows error code -1073741515 corresponding to hex error code 0xc0000135 emits when the necessary DLLs are not in the program’s working directory or on Path environment variable.
This will make CTest tests fail with error code 135.
The CMake generator expression
TARGET_RUNTIME_DLL_DIRS
along with test property
ENVIRONMENT_MODIFICATION
can be used to set the Path environment variable for the test, gathering all the directories of the DLLs CMake knows the target needs.
C++17 and C++20 standard code is used throughout projects of all sizes, perhaps with limited-feature fallback to older language standards.
Some standards certifications require a specific language standard.
High reliability and safety-critical projects may require specific language standards.
Examples include
FACE
and
MISRA C / C++.
To enforce a specific language standard be limited, consider in a header used throughout the project as follows. This example limits the language standard to C++14 or earlier by halt the build if a higher standard is detected:
#if __cplusplus >= 201703L
#error "C++14 or earlier required"
#endif
For C code say no higher than C99, consider in a header used throughout the project, which will halt the build if a higher standard is detected:
#if __STDC_VERSION__ >= 201112L
#error "C99 or earlier required"
#endif
Anaconda Python
conda activate
puts Conda directories first on environment variable PATH.
This leads CMake to prefer finding Anaconda binaries (find_library, find_program, …) and Anaconda GCC compilers (if installed) over later directories on system PATH.
Anaconda libraries and compilers are generally incompatible with the system or desired compiler.
For certain libraries like HDF5, Anaconda is particularly problematic at interfering with CMake.
Detect Anaconda environment by existence of environment variable
CONDA_PREFIX.
Fix by putting in CMakeLists.txt like the following.
cmake_minimum_required(VERSION...)# ignore Anaconda compilers, which are typically not compatible with the system
if(DEFINEDENV{CONDA_PREFIX})set(CMAKE_IGNORE_PATH $ENV{CONDA_PREFIX}/bin)endif()project(exampleLANGUAGESC)# Optional next two lines if needing Python in CMake project
unset(CMAKE_IGNORE_PATH)find_package(Python...)# end optional lines
# exclude Anaconda directories from search
if(DEFINEDENV{CONDA_PREFIX})list(APPENDCMAKE_IGNORE_PREFIX_PATH $ENV{CONDA_PREFIX})list(APPENDCMAKE_IGNORE_PATH $ENV{CONDA_PREFIX}/bin)# need CMAKE_IGNORE_PATH to ensure system env var PATH
# doesn't interfere despite CMAKE_IGNORE_PREFIX_PATH
endif()
