How do I define a C/C++ preprocessor variable in Meson?

Question

I want to conditionally define a variable that I then can use within C/C++ sources to conditionally compile some code, like this:

#ifdef MY_MESON_VARIABLE
    // some code
#endif

How do I go about actually setting MY_MESON_VARIABLE from Meson build system code such that it becomes accessible to the C preprocessor? I already know how do flow control in Meson, so I just need to know how to set a preprocessor variable.

Passing -DMU_MESON_VARIABLE (or /DMU_MESON_VARIABLE for visual) to the command line, your build system might have dedicated api to add those definitions. — Jarod42
– Jarod42, Commented Nov 6, 2024 at 11:05
@Jarod42 thanks, I guess it was hiding from me in plain sight. — Newbyte
– Newbyte, Commented Nov 6, 2024 at 11:13

Garnik · Accepted Answer · 2024-11-16 15:32:38Z

1

Meson allows you to define preprocessor variables via compilation arguments. To do this, use add_project_arguments or add_global_arguments, add to Meson.build:

add_project_arguments('-DMY_MESON_VARIABLE', language: 'c')

The -D before the variable name tells the compiler to define the specified variable.

The add_project_arguments function adds compilation arguments that will be applied to the entire project.

This will make MY_MESON_VARIABLE available for #ifdef in C/C++ sources.

answered Nov 16, 2024 at 15:32

Garnik

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