---
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
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](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,
vs2010, 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_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`.
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 modules](Reference-manual.md#shared_module) 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 |
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 `_*` 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 `_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.