Most non-trivial builds require user-settable options. As an example a
program may have two different data backends that are selectable at
build time. Meson provides for this by having a option definition
file. Its name is
meson_options.txt and it is placed at the root of
your source tree.
Here is a simple option file.
option('someoption', type : 'string', value : 'optval', description : 'An option') option('other_one', type : 'boolean', value : false) option('combo_opt', type : 'combo', choices : ['one', 'two', 'three'], value : 'three') option('integer_opt', type : 'integer', min : 0, max : 5, value : 3) # Since 0.45.0 option('free_array_opt', type : 'array', value : ['one', 'two']) # Since 0.44.0 option('array_opt', type : 'array', choices : ['one', 'two', 'three'], value : ['one', 'two']) option('some_feature', type : 'feature', value : 'enabled') # Since 0.47.0 option('long_desc', type : 'string', value : 'optval', description : 'An option with a very long description' + 'that does something in a specific context') # Since 0.55.0
For built-in options, see Built-in options.
Build option types
All types allow a
description value to be set describing the option,
if no description is set then the name of the option will be used instead.
The string type is a free form string. If the default value is not set then an empty string will be used as the default.
Booleans may have values of either
false. If no default
value is supplied then
true will be used as the default.
A combo allows any one of the values in the
choices parameter to be
selected. If no default value is set then the first value will be the
An integer option contains a single integer with optional upper and
lower values that are specified with the
This type is available since Meson version 0.45.0.
Arrays represent an array of strings. By default the array can contain
arbitrary strings. To limit the possible values that can used set the
choices parameter. Meson will then only allow the value array to
contain strings that are in the given list. The array may be
value parameter specifies the default value of the option
and if it is unset then the values of
choices will be used as the
As of 0.47.0 -Dopt= and -Dopt= both pass an empty list, before this -Dopt= would pass a list with an empty string.
This type is available since version 0.44.0
feature option has three states:
It is intended to be passed as value for the
argument of most functions. Currently supported in
enabledis the same as passing
required : true.
autois the same as passing
required : false.
disableddo not look for the dependency and always return 'not-found'.
When getting the value of this type of option using
special feature option
object is returned instead
of the string representation of the option's value. This object can be
d = dependency('foo', required : get_option('myfeature')) if d.found() app = executable('myapp', 'main.c', dependencies : [d]) endif
To check the value of the feature, the object has three methods returning a boolean and taking no argument:
This is useful for custom code depending on the feature:
if get_option('myfeature').enabled() # ... endif
If the value of a
feature option is set to
auto, that value is
overridden by the global
auto_features option (which defaults to
auto). This is intended to be used by packagers who want to have
full control on which dependencies are required and which are
disabled, and not rely on build-deps being installed (at the right
version) to get a feature enabled. They could set
auto_features=enabled to enable all features and disable explicitly
only the few they don't want, if any.
This type is available since version 0.47.0
Using build options
optval = get_option('opt_name')
This function also allows you to query the value of Meson's built-in project options. For example, to get the installation prefix you would issue the following command:
prefix = get_option('prefix')
It should be noted that you can not set option values in your Meson
scripts. They have to be set externally with the
command line tool. Running
meson configure without arguments in a
build dir shows you all options you can set.
To change their values use the
$ meson configure -Doption=newvalue
Setting the value of arrays is a bit special. If you only pass a single string, then it is considered to have all values separated by commas. Thus invoking the following command:
$ meson configure -Darray_opt=foo,bar
would set the value to an array of two elements,
If you need to have commas in your string values, then you need to pass the value with proper shell quoting like this:
$ meson configure "-Doption=['a,b', 'c,d']"
The inner values must always be single quotes and the outer ones double quotes.
To change values in subprojects prepend the name of the subproject and a colon:
$ meson configure -Dsubproject:option=newvalue
NOTE: If you cannot call
meson configure you likely have a old
version of Meson. In that case you can call
mesonconf instead, but
that is deprecated in newer versions
Yielding to superproject option
Suppose you have a master project and a subproject. In some cases it
might be useful to have an option that has the same value in both of
them. This can be achieved with the
yield keyword. Suppose you have
an option definition like this:
option('some_option', type : 'string', value : 'value', yield : true)
If you build this project on its own, this option behaves like
usual. However if you build this project as a subproject of another
project which also has an option called
some_option, then calling
get_option returns the value of the superproject. If the value of
get_option returns the value of the subproject's
Built-in build options
There are a number of built-in options. To get the
current list execute
meson configure in the build directory.
backend_startup_project option can be set to define the default
project that will be executed with the "Start debugging F5" action in
visual studio. It should be the same name as an executable target
project('my_project', 'c', default_options: ['backend_startup_project=my_exe']) executable('my_exe', ...)
backend_max_links can be set to limit the number of processes
that ninja will use to link.
The results of the search are