• -l for adding C library names that you want to get linked
• -L for adding C library files search paths
• -D for setting compile time variables

You can use different flags for different targets. Currently the linux, darwin , freebsd, and windows flags are supported.

NB: Each flag must go on its own line (for now)

Add #pkgconfig directive is used to tell the compiler which modules should be used for compiling and linking using the pkg-config files provided by the respective dependencies.

As long as backticks can’t be used in #flag and spawning processes is not desirable for security and portability reasons, V uses its own pkgconfig library that is compatible with the standard freedesktop one.

If no flags are passed it will add --cflags and --libs, both lines below do the same:

You can also include C code directly in your V module. For example, let’s say that your C code is located in a folder named ‘c’ inside your module folder. Then:

• Put a v.mod file inside the toplevel folder of your module (if you created your module with v new you already have v.mod file). For example:

NB: @VROOT will be replaced by V with the nearest parent folder, where there is a v.mod file. Any .v file beside or below the folder where the v.mod file is, can use #flag @VROOT/abc to refer to this folder. The @VROOT folder is also prepended to the module lookup path, so you can import other modules under your @VROOT, by just naming them.

The instructions above will make V look for an compiled .o file in your module folder/c/implementation.o. If V finds it, the .o file will get linked to the main executable, that used the module. If it does not find it, V assumes that there is a @VROOT/c/implementation.c file, and tries to compile it to a .o file, then will use that.

This allows you to have C code, that is contained in a V module, so that its distribution is easier. You can see a complete minimal example for using C code in a V wrapper module here: . Another example, demonstrating passing structs from C to V and back again: interoperate between C to V to C.

You can use -cflags to pass custom flags to the backend C compiler. You can also use -cc to change the default C backend compiler. For example: -cc gcc-9 -cflags -fsanitize=thread.

NB: The .vstring() and .vstring_with_len() methods do NOT create a copy of the cstring, so you should NOT free it after calling the method .vstring(). If you need to make a copy of the C string (some libc APIs like getenv pretty much require that, since they return pointers to internal libc memory), you can use cstring_to_vstring(cstring).

On Windows, C APIs often return so called strings (utf16 encoding). These can be converted to V strings with string_from_wide(&u16(cwidestring)) .

V has these types for easier interoperability with C:

• voidptr for C’s void*,
• byteptr for C’s byte* and
• charptr for C’s char*.
• &charptr for C’s char**

To cast a voidptr to a V reference, use user := &User(user_void_ptr).

voidptr can also be dereferenced into a V struct through casting: user := User(user_void_ptr).