If there are multiple configuration options, passing them through compiler flags becomes very burdensome. It also makes the configuration settings hard to inspect. To make things easier, Meson supports the generation of configure files. This feature is similar to one found in other build systems such as CMake.
Suppose we have the following Meson snippet:
conf_data = configuration_data() conf_data.set('version', '1.2.3') configure_file(input : 'config.h.in', output : 'config.h', configuration : conf_data)
and that the contents of
#define VERSION_STR "@version@"
Meson will then create a file called
config.h in the corresponding
build directory whose contents are the following.
#define VERSION_STR "1.2.3"
More specifically, Meson will find all strings of the type
and replace them with respective values set in
conf_data. You can
use a single
configuration_data object as many times as you like,
but it becomes immutable after being passed to the
function. That is, after it has been used once to generate output the
set function becomes unusable and trying to call it causes an error.
For more complex configuration file generation Meson provides a second form. To use it, put a line like this in your configuration file.
The replacement that happens depends on what the value and type of TOKEN is:
#define TOKEN // If TOKEN is set to boolean true. #undef TOKEN // If TOKEN is set to boolean false. #define TOKEN 4 // If TOKEN is set to an integer or string value. /* undef TOKEN */ // If TOKEN has not been set to any value.
Note that if you want to define a C string, you need to do the quoting yourself like this:
Since this is such a common operation, Meson provides a convenience method:
plain_var = 'value' conf_data.set_quoted('TOKEN', plain_var) # becomes #define TOKEN "value"
Often you have a boolean value in Meson but need to define the C/C++ token as 0 or 1. Meson provides a convenience function for this use case.
conf_data.set10(token, boolean_value) # The line above is equivalent to this: if boolean_value conf_data.set(token, 1) else conf_data.set(token, 0) endif
Configuring without an input file
If the input file is not defined then Meson will generate a header
file all the entries in the configuration data object. The
replacements are the same as when generating
conf_data.set('FOO', '"string"') => #define FOO "string" conf_data.set('FOO', 'a_token') => #define FOO a_token conf_data.set('FOO', true) => #define FOO conf_data.set('FOO', false) => #undef FOO conf_data.set('FOO', 1) => #define FOO 1 conf_data.set('FOO', 0) => #define FOO 0
In this mode, you can also specify a comment which will be placed before the value so that your generated files are self-documenting.
conf_data.set('BAR', true, description : 'Set BAR if it is available')
/* Set BAR if it is available */ #define BAR
A full example
Generating and using a configuration file requires the following steps:
- generate the file
- create an include directory object for the directory that holds the file
- use it in a target
We are going to use the traditional approach of generating a header
file in the top directory. The common name is
config.h but we're
going to use an unique name. This avoids the problem of accidentally
including the wrong header file when building a project with many
At the top level we generate the file:
conf_data = configuration_data() # Set data configure_file(input : 'projconfig.h.in', output : 'projconfig.h', configuration : conf_data)
Immediately afterwards we generate the include object.
configuration_inc = include_directories('.')
Finally we specify this in a target that can be in any subdirectory.
executable(..., include_directories : configuration_inc)
Now any source file in this target can include the configuration header like this:
The results of the search are