Not all compilers and platforms are alike. Therefore Meson provides the tools to detect properties of the system during configure time. To get most of this information, you first need to extract the compiler object from the main meson variable.
compiler = meson.get_compiler('c')
Here we extract the C compiler. We could also have given the argument cpp to get the C++ compiler, objc to get the objective C compiler and so on. The call is valid for all languages specified in the project declaration. Trying to obtain some other compiler will lead to an unrecoverable error.
This is a bit complex and more thoroughly explained on the page on cross compilation. But if you just want to know the operating system your code will run on, issue this command:
host_machine.system()
The compiler object has a method called get_id, which returns a lower case string describing the “family” of the compiler. See reference tables for a list of supported compiler ids.
Sometimes the only way to test the system is to try to compile some sample code and see if it works. This is a two-phase operation. First we define some code using the multiline string operator:
code = '''#include<stdio.h> void func() { printf("Compile me.\n"); } '''
Then we can run the test.
result = compiler.compiles(code, name : 'basic check')
The variable result will now contain either true or false depending on whether the compilation succeeded or not. The keyword argument name is optional. If it is specified, Meson will write the result of the check to its log.
Sometimes it is necessary to check whether a certain code fragment not only compiles, but also links successfully, e.g. to check if a symbol is actually present in a library. This can be done using the ‘‘‘.links()’’’ method on a compiler object like this:
code = '''#include<stdio.h> void func() { printf("Compile me.\n"); } '''
Then we can run the test.
result = compiler.links(code, args : '-lfoo', name : 'link check')
The variable result will now contain either true or false depending on whether the compilation and linking succeeded or not. The keyword argument name is optional. If it is specified, Meson will write the result of the check to its log.
Here is how you would compile and run a small test application.
code = '''#include<stdio.h> int main(int argc, char **argv) { printf("%s\n", "stdout"); fprintf(stderr, "%s\n", "stderr"); return 0; } ''' result = compiler.run(code, name : 'basic check')
The result variable encapsulates the state of the test, which can be extracted with the following methods. The name keyword argument works the same as with compiles.
| Method | Return value |
|---|---|
| compiled | True if compilation succeeded. If false then all other methods return undefined values. |
| returncode | The return code of the application as an integer |
| stdout | Program's standard out as text. |
| stderr | Program's standard error as text. |
Here is an example usage:
if result.stdout().strip() == 'some_value' # do something endif
Header files provided by different platforms vary quite a lot. Meson has functionality to detect whether a given header file is available on the system. The test is done by trying to compile a simple test program that includes the specified header. The following snippet describes how this feature can be used.
if compiler.has_header('sys/fstat.h') # header exists, do something endif
Often you need to determine the size of a particular element (such as int, wchar_t or char*). Using the compiler variable mentioned above, the check can be done like this.
wcharsize = compiler.sizeof('wchar_t', prefix : '#include<wchar.h>')
This will put the size of wchar_t as reported by sizeof into variable wcharsize. The keyword argument prefix is optional. If specified its contents is put at the top of the source file. This argument is typically used for setting #include directives in configuration files.
In older versions (<= 0.30) meson would error out if the size could not be determined. Since version 0.31 it returns -1 if the size could not be determined.
Just having a header doesn't say anything about its contents. Sometimes you need to explicitly check if some function exists. This is how we would check whether the function somefunc exists in header someheader.h
if compiler.has_function('somefunc', prefix : '#include<someheader.h>') # function exists, do whatever is required. endif
Some platforms have different standard structures. Here's how one would check if a struct called mystruct from header myheader.h contains a member called some_member.
if compiler.has_member('struct mystruct', 'some_member', prefix : '#include<myheader.h>') # member exists, do whatever is required endif
Most platforms can't access some data types at any address. For example it is common that a char can be at any address but a 32 bit integer only at locations which are divisible by four. Determining the alignment of data types is simple.
int_alignment = compiler.alignment('int') # Will most likely contain the value 4.
This method tests if the compiler supports a given command line argument. This is implemented by compiling a small file with the given argument.
has_special_flags = compiler.has_argument('-Wspecialthing')
Note: some compilers silently swallow command line arguments they do not understand. Thus this test can not be made 100% reliable.