Environment specific files

V provides the ability to create files that will only be used in a specific environment. For example, only on Windows, or only on Linux.

If a file has an environment-specific suffix, it will only be compiled for that environment.

  • .js.v – will be used only by the JS backend. These files can contain JS.* declarations.
  • .c.v – will be used only by the C backend. These files can contain C.* declarations.
  • .native.v – will be used only by V's native backend.
  • _nix.c.v – will be used only on Unix systems (non-Windows).
  • _${os}.c.v – will be used only on the specific os system. For example, _windows.c.v will be used only when compiling on Windows, or with -os windows.
  • _default.c.v – will be used only if there is NOT a more specific platform file. For example, if you have both file_linux.c.v and file_default.c.v, and you are compiling for linux, then only file_linux.c.v will be used, and file_default.c.v will be ignored.

Here is a more complete example:


module main fn main() { println(message) }


module main const ( message = 'Hello, World!' )


module main const ( message = 'Hello, Linux!' )


module main const ( message = 'Hello, Windows!' )

With the example above:

  • when you compile for Windows, you will get 'Hello, Windows!'
  • when you compile for Linux, you will get 'Hello, Linux!'
  • when you compile for any other platform, you will get the non-specific 'Hello, World!' message.

_d_customflag.v – will be used only if you pass -d customflag to V. That corresponds to $if customflag ? {}, but for a whole file, not just a single block. customflag should be a snake_case identifier, it can not contain arbitrary characters (only lower case latin letters + numbers + _).

A combinatorial _d_customflag_linux.c.v postfix will not work. If you do need a custom flag file, that has platform dependent code, use the postfix _d_customflag.v, and then use platform dependent compile time conditional blocks inside it, i.e. $if linux {} etc.

_notd_customflag.v – similar to _d_customflag.v, but will be used only if you do NOT pass -d customflag to V.

See also Cross Compilation.