--- 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_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`. * < 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) 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 | | 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 `_*` 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.