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---
short-description: Built-in options to configure project properties
...
# Built-in options
Meson provides two kinds of options: [build options provided by the
build files](Build-options.md) 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.
### 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](Cross-compilation.md#defining-the-environment), 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](#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,<br>vs2010, vs2012, vs2013, vs2015, vs2017, vs2019, vs2022, xcode} | ninja | Backend to use | no | no |
| buildtype {plain, debug,<br>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 {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} | 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,<br>nodownload, forcefallback, nopromote} | default | Wrap mode to use | no | no |
| force_fallback_for | [] | Force fallback for those dependencies | no | no |
<a name="build-type-options"></a> 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 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_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](https://clang.llvm.org/docs/ThinLTO.html)
<a name="b_vscrt-from_buildtype"></a>
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 <br/>c++2a, c++1z, gnu++03, gnu++11, gnu++14, gnu++17, gnu++1z, <br/> 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](#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.
Since *0.63.0* all compiler options can be set per subproject, see
[here](#specifying-options-per-subproject) for details on how the default value
is inherited from 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
subproject's `default_options` is now respected.
## 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`).
### 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()`](Pkgconfig-module.md) and affect how the
`prefix` in the generated pkgconfig file is set (not to be confused
with the [install prefix](#directories)). 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 |
| ------ | ------------- | ----------------- | ----------- |
| 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) |
*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`.
*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`.
|
