Built-in options

Meson provides two kinds of options: build options provided by the build files and built-in options that are either universal options, base options, compiler options.

Universal options

A list of these options can be found by running meson --help. All these can be set by passing -Doption=value to meson (aka meson setup), or by setting them inside default_options of project() in your meson.build. Some options can also be set by --option=value, or --option value--- a list is shown by running meson setup --help.

For legacy reasons --warnlevel is the cli argument for the warning_level option.

They can also be edited after setup using meson configure -Doption=value.

Installation options are all relative to the prefix, except:

• When the prefix is /usr: sysconfdir defaults to /etc,
• localstatedir defaults to /var, and sharedstatedir defaults to
• /var/lib When the prefix is /usr/local: localstatedir defaults
• to /var/local, and sharedstatedir defaults to /var/local/lib

Directories

Option	Default value	Description
prefix	see below	Installation prefix
bindir	bin	Executable directory
datadir	share	Data file directory
includedir	include	Header file directory
infodir	share/info	Info page directory
libdir	see below	Library directory
libexecdir	libexec	Library executable directory
localedir	share/locale	Locale data directory
localstatedir	var	Localstate data directory
mandir	share/man	Manual page directory
sbindir	sbin	System executable directory
sharedstatedir	com	Architecture-independent data directory
sysconfdir	etc	Sysconf data directory

prefix defaults to C:/ on Windows, and /usr/local otherwise. You should always override this value.

libdir is automatically detected based on your platform, it should be correct when doing "native" (build machine == host machine) compilation. For cross compiles Meson will try to guess the correct libdir, but it may not be accurate, especially on Linux where different distributions have different defaults. Using a cross file, particularly the paths section may be necessary.

Core options

Options that are labeled "per machine" in the table are set per machine. See the specifying options per machine section for details.

Option	Default value	Description	Is per machine	Is per subproject
auto_features {enabled, disabled, auto}	auto	Override value of all 'auto' features	no	no
backend {ninja, vs, vs2010, vs2012, vs2013, vs2015, vs2017, vs2019, xcode}	ninja	Backend to use	no	no
buildtype {plain, debug, debugoptimized, release, minsize, custom}	debug	Build type to use	no	no
debug	true	Debug	no	no
default_library {shared, static, both}	shared	Default library type	no	yes
errorlogs	true	Whether to print the logs from failing tests.	no	no
install_umask {preserve, 0000-0777}	022	Default umask to apply on permissions of installed files	no	no
layout {mirror,flat}	mirror	Build directory layout	no	no
optimization {0, g, 1, 2, 3, s}	0	Optimization level	no	no
pkg_config_path {OS separated path}	''	Additional paths for pkg-config to search before builtin paths	yes	no
cmake_prefix_path	[]	Additional prefixes for cmake to search before builtin paths	yes	no
stdsplit	true	Split stdout and stderr in test logs	no	no
strip	false	Strip targets on install	no	no
unity {on, off, subprojects}	off	Unity build	no	no
unity_size {>=2}	4	Unity file block size	no	no
warning_level {0, 1, 2, 3}	1	Set the warning level. From 0 = none to 3 = highest	no	yes
werror	false	Treat warnings as errors	no	yes
wrap_mode {default, nofallback, nodownload, forcefallback, nopromote}	default	Wrap mode to use	no	no
force_fallback_for	[]	Force fallback for those dependencies	no	no

For setting optimization levels and toggling debug, you can either set the buildtype option, or you can set the optimization and debug options which give finer control over the same. Whichever you decide to use, the other will be deduced from it. For example, -Dbuildtype=debugoptimized is the same as -Ddebug=true -Doptimization=2 and vice-versa. This table documents the two-way mapping:

buildtype	debug	optimization
plain	false	0
debug	true	0
debugoptimized	true	2
release	false	3
minsize	true	s

All other combinations of debug and optimization set buildtype to 'custom'.

Base options

These are set in the same way as universal options, either by -Doption=value, or by setting them inside default_options of project() in your meson.build. However, they cannot be shown in the output of meson --help because they depend on both the current platform and the compiler that will be selected. The only way to see them is to setup a builddir and then run meson configure on it with no options.

The following options are available. Note that they may not be available on all platforms or with all compilers:

Option	Default value	Possible values	Description
b_asneeded	true	true, false	Use -Wl,--as-needed when linking
b_bitcode	false	true, false	Embed Apple bitcode, see below
b_colorout	always	auto, always, never	Use colored output
b_coverage	false	true, false	Enable coverage tracking
b_lundef	true	true, false	Don't allow undefined symbols when linking
b_lto	false	true, false	Use link time optimization
b_lto_threads	0	Any integer*	Use multiple threads for lto. (Added in 0.57.0)
b_lto_mode	default	default, thin	Select between lto modes, thin and default. (Added in 0.57.0)
b_ndebug	false	true, false, if-release	Disable asserts
b_pch	true	true, false	Use precompiled headers
b_pgo	off	off, generate, use	Use profile guided optimization
b_sanitize	none	see below	Code sanitizer to use
b_staticpic	true	true, false	Build static libraries as position independent
b_pie	false	true, false	Build position-independent executables (since 0.49.0)
b_vscrt	from_buildtype	none, md, mdd, mt, mtd, from_buildtype, static_from_buildtype	VS runtime library to use (since 0.48.0) (static_from_buildtype since 0.56.0)

The value of b_sanitize can be one of: none, address, thread, undefined, memory, address,undefined, but note that some compilers might not support all of them. For example Visual Studio only supports the address sanitizer.

• < 0 means disable, == 0 means automatic selection, > 0 sets a specific number to use

LLVM supports thin lto, for more discussion see LLVM's documentation

The default value of b_vscrt is from_buildtype. The following table is used internally to pick the CRT compiler arguments for from_buildtype or static_from_buildtype (since 0.56) based on the value of the buildtype option:

buildtype	from_buildtype	static_from_buildtype
debug	/MDd	/MTd
debugoptimized	/MD	/MT
release	/MD	/MT
minsize	/MD	/MT
custom	error!	error!

Notes about Apple Bitcode support

b_bitcode will pass -fembed-bitcode while compiling and will pass -Wl,-bitcode_bundle while linking. These options are incompatible with b_asneeded, so that option will be silently disabled.

shared_module()s will not have bitcode embedded because -Wl,-bitcode_bundle is incompatible with both -bundle and -Wl,-undefined,dynamic_lookup which are necessary for shared modules to work.

Compiler options

Same caveats as base options above.

The following options are available. They can be set by passing -Doption=value to meson. Note that both the options themselves and the possible values they can take will depend on the target platform or compiler being used:

Option	Default value	Possible values	Description
c_args		free-form comma-separated list	C compile arguments to use
c_link_args		free-form comma-separated list	C link arguments to use
c_std	none	none, c89, c99, c11, c17, c18, c2x, gnu89, gnu99, gnu11, gnu17, gnu18, gnu2x	C language standard to use
c_winlibs	see below	free-form comma-separated list	Standard Windows libs to link against
c_thread_count	4	integer value ≥ 0	Number of threads to use with emcc when using threads
cpp_args		free-form comma-separated list	C++ compile arguments to use
cpp_link_args		free-form comma-separated list	C++ link arguments to use
cpp_std	none	none, c++98, c++03, c++11, c++14, c++17, c++20 c++2a, c++1z, gnu++03, gnu++11, gnu++14, gnu++17, gnu++1z, gnu++2a, gnu++20, vc++14, vc++17, vc++latest	C++ language standard to use
cpp_debugstl	false	true, false	C++ STL debug mode
cpp_eh	default	none, default, a, s, sc	C++ exception handling type
cpp_rtti	true	true, false	Whether to enable RTTI (runtime type identification)
cpp_thread_count	4	integer value ≥ 0	Number of threads to use with emcc when using threads
cpp_winlibs	see below	free-form comma-separated list	Standard Windows libs to link against
fortran_std	none	[none, legacy, f95, f2003, f2008, f2018]	Fortran language standard to use
cuda_ccbindir		filesystem path	CUDA non-default toolchain directory to use (-ccbin) (Added in 0.57.1)

The default values of c_winlibs and cpp_winlibs are in compiler-specific argument forms, but the libraries are: kernel32, user32, gdi32, winspool, shell32, ole32, oleaut32, uuid, comdlg32, advapi32.

All these <lang>_* options are specified per machine. See below in the specifying options per machine section on how to do this in cross builds.

When using MSVC, cpp_eh=none will result in no exception flags being passed, while the cpp_eh=[value] will result in /EH[value]. Since 0.51.0 cpp_eh=default will result in /EHsc on MSVC. When using gcc-style compilers, nothing is passed (allowing exceptions to work), while cpp_eh=none passes -fno-exceptions.

Since 0.54.0 The <lang>_thread_count option can be used to control the value passed to -s PTHREAD_POOL_SIZE when using emcc. No other c/c++ compiler supports this option.

Specifying options per machine

Since 0.51.0, some options are specified per machine rather than globally for all machine configurations. Prefixing the option with build. just affects the build machine configuration, while unprefixed just affects the host machine configuration, respectively. For example:

• build.pkg_config_path controls the paths pkg-config will search for just native: true dependencies (build machine).

• pkg_config_path controls the paths pkg-config will search for just native: false dependencies (host machine).

This is useful for cross builds. In the native builds, build = host, and the unprefixed option alone will suffice.

Prior to 0.51.0, these options just effected native builds when specified on the command line, as there was no build. prefix. Similarly named fields in the [properties] section of the cross file would effect cross compilers, but the code paths were fairly different allowing differences in behavior to crop out.

Specifying options per subproject

Since 0.54.0 default_library and werror built-in options can be defined per subproject. This is useful for example when building shared libraries in the main project, but static link a subproject, or when the main project must build with no warnings but some subprojects cannot.

Most of the time this would be used either by the parent project by setting subproject's default_options (e.g. subproject('foo', default_options: 'default_library=static')), or by the user using the command line -Dfoo:default_library=static.

The value is overridden in this order:

• Value from parent project
• Value from subproject's default_options if set
• Value from subproject() default_options if set
• Value from command line if set

Since 0.56.0 warning_level can also be defined per subproject.

Module options

Some Meson modules have built-in options. They can be set by prefixing the option name with the module name: -D<module>.<option>=<value> (e.g. -Dpython.platlibdir=/foo).

Python module

Option	Default value	Possible values	Description
platlibdir		Directory path	Directory for site-specific, platform-specific files (Since 0.60.0)
purelibdir		Directory path	Directory for site-specific, non-platform-specific files (Since 0.60.0)

Since 0.60.0 python.platlibdir and python.purelibdir options are used by python module methods python.install_sources() and python.get_install_dir(). By default Meson tries to detect the correct installation path, but make them relative to the installation prefix, which will often result in installed python modules to not be found by the interpreter unless prefix is /usr on Linux, or for example C:\Python39 on Windows. These options can be absolute paths outside of prefix.