Often you need to specify extra compiler arguments. Meson provides two different ways to achieve this: global arguments and per-target arguments.
Global compiler arguments are set with the following command. As an example you could do this.
add_global_arguments('-DFOO=bar', language : 'c')
This makes Meson add the define to all C compilations. Usually you
would use this setting for flags for global settings. Note that for
setting the C/C++ language standard (the
-std=c99 argument in GCC),
you would probably want to use a default option of the
function. For details see the reference manual.
Global arguments have certain limitations. They all have to be defined before any build targets are specified. This ensures that the global flags are the same for every single source file built in the entire project with one exception. Compilation tests that are run as part of your project configuration do not use these flags. The reason for that is that you may need to run a test compile with and without a given flag to determine your build setup. For this reason tests do not use these global arguments.
You should set only the most essential flags with this setting, you should not set debug or optimization flags. Instead they should be specified by selecting an appropriate build type.
Project arguments work similar to global arguments except that they are valid only within the current subproject. The usage is simple:
add_project_arguments('-DMYPROJ=projname', language : 'c')
This would add the compiler flags to all C sources in the current project.
Per target arguments
Per target arguments are just as simple to define.
executable('prog', 'prog.cc', cpp_args : '-DCPPTHING')
Here we create a C++ executable with an extra argument that is used during compilation but not for linking.
You can find the parameter name for other languages in the reference tables.
Specifying extra linker arguments is done in the same way:
executable('prog', 'prog.cc', link_args : '-Wl,--linker-option')
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