Organization
- Directories that contain CMakeLists.txt are the entry point for the build system generator. Subdirectories can be added with the add_subdirectory() and must contain a CMakeLists.txt too.
- Scripts are <script>.cmake files that can be executed with the cmake -P <script>.cmake. Not all commands are supported.
- Modules are <script>.cmake files located in the CMAKE_MODULE_PATH. MOdules can be loaded with the include() command.
Commands
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command_name(space seperated list of strings)
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- Scripting commands change the state of command processor
- set variables
- change behavior of other commands
- Project commands
- create build targets
- modify build targets
- Command invocations are not expressions.
Variables
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set(myvar world)
message(STATUS "hello ${myvar})
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- Set withe the set() command.
- Expand with ${}.
- Variables and values are strings.
- Lists are ; seperated strings.
- CMake variables are not environment variables (unlike Makefile).
- Unset variable expands to empty string.
Comments
Use # for single line comments.
Custom Functions/Macros
- Commands can be added with function() or macro().
- When a new command replaces an existing command, the old one can be accessed with a _ prefix.
function(my_command input output)
# some comment
set(${output} ... PARENT_SCOPE)
endfunction()
my_command(foo bar)
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- Variables are scoped to the function unless set with the PARENT_SCOPE.
- Available variables: input, output, ARGC, ARGN, ARG0, ARG1, ...
- Example: ${output} expands to bar.
macro(my_command input output)
# some comment
endmacro()
my_command(foo bar)
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- No extra scope with macros.
- Text replacements: ${input}, ${output}, ${ARGC}, ${ARGV}, ${ARGN}, ${ARG0}, ...
- Example: ${output} is replace by bar.
CREATE macros to wrap commands that have output parameters. Otherwise, create functions.
References
https://www.youtube.com/watch?v=bsXLMQ6WgIk