Learning CMake
This morning I spent time just sitting and reading about CMake. A lot of this infomration is well known and probably obvious to anybody who’s been dealing with CMake, but hey, we all gotta start from somewhere, right?
I started making my way through the CMake documentation at https://cmake.org/cmake/help/latest/.
Some gems:
introduction-to-cmake-buildsystems: a project may specify its buildsystem abstractly using files written in the CMake language. CMake input files are written in the “CMake Language” in source files named CMakeLists.txt or ending in a .cmake file name extension.
variable-references An environment variable reference has the form $ENV{
}. See the Environment Variables section for more information.
lists a string may be treated as a list in certain contexts,
So lists are just special strings? Interesting.
lists a string may be treated as a list in certain contexts, In function() implementations, avoid ARGV and ARGN, which do not distinguish semicolons in values from those separating values. Instead, prefer using named positional arguments and the ARGC and ARGV# variables. When using cmake_parse_arguments() to parse arguments, prefer its PARSE_ARGV signature, which uses the ARGV# variables.
Gotta keep this in mind.
directories “This file may contain the entire build specification or use the add_subdirectory() command to add subdirectories to the build.”
This allows directories to be the general “separation of concerns” - means cmake tends towards putting thing in directories as separation.
Requirements for a Library Remember INTERFACE means things that consumers require but the producer doesn’t.
variable-references Directory Scope Each of the Directories in a source tree has its own variable bindings. Before processing the CMakeLists.txt file for a directory, CMake copies all variable bindings currently defined in the parent directory, if any, to initialize the new directory scope.
So CMake is a set of commands that run after one another. And directories can be added. Ok, let’s see if this works.
➜ testing_cmake1 ls
CMakeLists.txt subdir
➜ testing_cmake1 cat CMakeLists.txt
cmake_minimum_required(VERSION 3.10)
# set the project name
project(testing_cmake1)
message("Before Project: ${PROJECT_NAME} CMake Project: ${CMAKE_PROJECT_NAME}")
add_subdirectory(subdir)
message("After Project: ${PROJECT_NAME} CMake Project: ${CMAKE_PROJECT_NAME}")
➜ testing_cmake1 cat subdir/CMakeLists.txt
cmake_minimum_required(VERSION 3.10)
message("subdir: Before Project: ${PROJECT_NAME} CMake Project: ${CMAKE_PROJECT_NAME}")
# set the project name
project(subdir)
message("subdir: After Project: ${PROJECT_NAME} CMake Project: ${CMAKE_PROJECT_NAME}")
➜ testing_cmake1 mkdir build; pushd build; cmake ..
/tmp/testing_cmake/testing_cmake1/build /tmp/testing_cmake/testing_cmake1 /tmp/testing_cmake /tmp/testing_cmake/doubleit /tmp/testing_cmake/doubleit/build /tmp ~/Development/github.com/rmpowell77/rmpowell77.github.io.git ~/Development/github.com/rmpowell77 ~/Development/github.com/rmpowell77/rmpowell77.github.io.git/_posts ~/Development/github.com/calband/calchart.git/build5
-- The C compiler identification is AppleClang 13.1.6.13160021
-- The CXX compiler identification is AppleClang 13.1.6.13160021
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
Before Project: testing_cmake1 CMake Project: testing_cmake1
subdir: Before Project: testing_cmake1 CMake Project: testing_cmake1
subdir: After Project: subdir CMake Project: testing_cmake1
After Project: testing_cmake1 CMake Project: testing_cmake1
-- Configuring done
-- Generating done
-- Build files have been written to: /tmp/testing_cmake/testing_cmake1/build
Basically gave me what I was looking for. In subdirectories it inherits all the variable names, and then creates new ones when they are created.
Next, I’m going to work through the tutorial. It’s great.
Very cool tool: ccmake