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

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 usually relative to the prefix but it should not be relied on, since they can be absolute paths in the following cases:

  • 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
  • When an absolute path outside of prefix is provided by the user/distributor.


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
licensedir see below Licenses directory (since 1.1.0)
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.

licensedir is empty by default. If set, it defines the default location to install a dependency manifest and project licenses. For more details, see meson.install_dependency_manifest().

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, vs2022, xcode, none}
ninja Backend to use no no
genvslite {vs2022} vs2022 Setup multi-builtype ninja build directories and Visual Studio solution no no
buildtype {plain, debug,
debugoptimized, release, minsize, custom}
debug Build type to use no no
debug true Enable debug symbols and other information 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 {plain, 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
prefer_static false Whether to try static linking before shared linking no 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, everything} 1 Set the warning level. From 0 = compiler default to everything = 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
vsenv false Activate Visual Studio environment no no

Details for backend

Several build file formats are supported as command runners to build the configured project. Meson prefers ninja by default, but platform-specific backends are also available for better IDE integration with native tooling: Visual Studio for Windows, and xcode for macOS. It is also possible to configure with no backend at all, which is an error if you have targets to build, but for projects that need configuration + testing + installation allows for a lighter automated build pipeline.

Details for genvslite

Setup multiple buildtype-suffixed, ninja-backend build directories (e.g. [builddir]_[debug/release/etc.]) and generate [builddir]_vs containing a Visual Studio solution with multiple configurations that invoke a meson compile of the setup build directories, as appropriate for the current configuration (builtype).

This has the effect of a simple setup macro of multiple 'meson setup ...' invocations with a set of different buildtype values. E.g. meson setup ... --genvslite vs2022 somebuilddir does the following -

meson setup ... --backend ninja --buildtype debug somebuilddir_debug
meson setup ... --backend ninja --buildtype debugoptimized somebuilddir_debugoptimized
meson setup ... --backend ninja --buildtype release somebuilddir_release

and additionally creates another 'somebuilddir_vs' directory that contains a generated multi-configuration visual studio solution and project(s) that are set to build/compile with the somebuilddir_[...] that's appropriate for the solution's selected buildtype configuration.

Details for buildtype

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

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

Details for warning_level

Exact flags per warning level is compiler specific, but there is an approximative table for most common compilers.

Warning level GCC/Clang MSVC
1 -Wall /W2
2 -Wall -Wextra /W3
3 -Wall -Wextra -Wpedantic /W4
everything -Weverything /Wall

Clang's -Weverything is emulated on GCC by passing all known warning flags.

Details for vsenv

The --vsenv argument is supported since 0.60.0, -Dvsenv=true syntax is supported since 1.1.0.

Since 0.59.0, meson automatically activates a Visual Studio environment on Windows for all its subcommands, but only if no other compilers (e.g. gcc or clang) are found, and silently continues if Visual Studio activation fails.

Setting the vsenv option to true forces Visual Studio activation even when other compilers are found. It also make Meson abort with an error message when activation fails.

vsenv is true by default when using the vs backend.

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 setup --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_thinlto_cache false true, false Enable LLVM's ThinLTO cache for faster incremental builds. (Added in 0.64.0)
b_thinlto_cache_dir (Internal build dir) true, false Specify where to store ThinLTO cache objects. (Added in 0.64.0)
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, leak, 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, c23, gnu89, gnu99, gnu11, gnu17, gnu18, gnu2x, gnu23 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++20, 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=[value] will result in /EH[value] being passed. The magic value none translates to s-c- to disable exceptions. Since 0.51.0 default translates to sc. 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.

Since 0.63.0 all compiler options can be set per subproject, see here for details on how the default value is inherited from the main project. This is useful, for example, when the main project requires C++11, but a subproject requires C++14. The cpp_std value from the subproject's default_options is now respected.

Since 1.3.0 c_std and cpp_std options now accept a list of values. Projects that prefer GNU C, but can fallback to ISO C, can now set, for example, default_options: 'c_std=gnu11,c11', and it will use gnu11 when available, but fallback to c11 otherwise. It is an error only if none of the values are supported by the current compiler. Likewise, a project that can take benefit of c++17 but can still build with c++11 can set default_options: 'cpp_std=c++17,c++11'. This allows us to deprecate gnuXX values from the MSVC compiler. That means that default_options: 'c_std=gnu11' will now print a warning with MSVC but fallback to c11. No warning is printed if at least one of the values is valid, i.e. default_options: 'c_std=gnu11,c11'. In the future that deprecation warning will become an hard error because c_std=gnu11 should mean GNU is required, for projects that cannot be built with MSVC for example.

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. only affects the build machine configuration, while leaving it unprefixed only affects the host machine configuration. For example:

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

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

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

Prior to 0.51.0, these options only affected 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 affect 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 and statically linking 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 in the parent project by setting subproject's default_options (e.g. subproject('foo', default_options: 'default_library=static')), or by the user through 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 with the module's name: -D<module>.<option>=<value> (e.g. -Dpython.platlibdir=/foo).

Pkgconfig module

Option Default value Possible values Description
relocatable false true, false Generate the pkgconfig files as relocatable (Since 0.63.0)

Since 0.63.0 The pkgconfig.relocatable option is used by the pkgconfig module–namely pkg.generate()–and affects how the prefix (not to be confused with the install prefix) in the generated pkgconfig file is set. When it is true, the prefix will be relative to the install_dir-this allows the pkgconfig file to be moved around and still work, as long as the relative path is not broken. In general, this allows for the whole installed package to be placed anywhere on the system and still work as a dependency. When it is set to false, the prefix will be the same as the install prefix.

An error will be raised if pkgconfig.relocatable is true and the install_dir for a generated pkgconfig file points outside the install prefix. For example: if the install prefix is /usr and the install_dir for a pkgconfig file is /var/lib/pkgconfig.

Python module

Option Default value Possible values Description
bytecompile 0 integer from -1 to 2 What bytecode optimization level to use (Since 1.2.0)
install_env prefix {auto,prefix,system,venv} Which python environment to install to (Since 0.62.0)
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)
allow_limited_api true true, false Disables project-wide use of the Python Limited API (Since 1.3.0)

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

Since 0.62.0 The python.install_env option is used to detect the correct installation path. Setting to system will avoid making the paths relative to prefix and instead use the global site-packages of the selected python interpreter directly, even if it is a venv. Setting to venv will instead use the paths for the virtualenv the python found installation comes from (or fail if it is not a virtualenv). Setting to auto will check if the found installation is a virtualenv, and use venv or system as appropriate (but never prefix). This option is mutually exclusive with the platlibdir/purelibdir.

For backwards compatibility purposes, the default install_env is prefix.

Since 1.2.0 The python.bytecompile option can be used to enable compiling python bytecode. Bytecode has 3 optimization levels:

  • 0, bytecode without optimizations
  • 1, bytecode with some optimizations
  • 2, bytecode with some more optimizations

To this, Meson adds level -1, which is to not attempt to compile bytecode at all.

Since 1.3.0 The python.allow_limited_api option affects whether the limited_api keyword argument of the extension_module method is respected. If set to false, the effect of the limited_api argument is disabled.

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