Ardour Code Style

That said, this isn't meant to be a strict listing of how your code must be. It is intended to help your code fit in with the rest of the Ardour codebase. This is the style that we have evolved to.

  1. Any header that is included from a part of the Ardour source tree MUST be included using quotes, not angle brackets. Angle bracket includes are for out-of-tree ('system') includes ONLY.
  2. List included header files in alphabetical order within the following categories (in this order): C++ headers (e.g. <cstdlib>), C headers (e.g. <sys/time.h>), Boost headers, other non-GUI 3rd party library headers, libpbd headers, libmidi++ headers, GTK headers, gtkmm headers, all others.
  3. In Python files, use spaces, not tabs. Tabs seem to get a little messed up and spaces are more rigorous where it is important.
  4. Always use curly braces with if-, for-, do-, and while-statements.
  5. Since this is C++, use 0, not NULL.
  6. Similarly, use true/false, not TRUE/FALSE
  7. If an argument is being passed by reference, and cannot be null, always pass it as a reference, not a pointer.
  8. Prefer references over pointers
  9. For core (libardour) data structures, prefer shared_ptr to manage lifetimes
  10. Never, ever bind a shared_ptr to a sigc::signal. Always convert to a weak_ptr first.
  11. In GNU Emacs, use the "linux" C and C++ mode style
  12. When incrementing any STL iterator, always use ++iter, not iter++
  13. When looping over any STL container and performing operations on its contents or iterators to it, always consider the possibility that the operation may remove items from the container and thus invalidate the iterator you are currently operating on. The typical approach looks like this:
       for (iter = container.begin(); iter != container.end(); ) {
           Iterator tmp;
       tmp = iter;
        .... do something ...
       iter = tmp;


    Another approach looks like:
    for (iter = container.begin(); iter != container.end(); ) {
           if (... iter matches some condition ...) {
                   iter = container.erase (iter);
           } else {
  14. Because of the previous issue, generally prefer std::list over std::vector. Erasing an element within a vector invalidates iterators to all later elements. Use vector only when confident that this issue doesn't exist.
  15. Class types have names like SomeClassType; variables have names like a_pleasant_name.
  16. Use const wherever possible.
  17. Throw PBD::failed_constructor to exit constructors abnormally, and catch this exception.
  18. That said, attempt to perform object initialization in an init function that is called post-construction. See Meyers for more information on this pattern.
  19. Use cstdio, not stdio.h style standard includes.
  20. Never declare using namespace in a header.
  21. Don't even think of using Microsoft-style "Hungarian" notation
  22. When constructing paths ("filenames") do not include separators ("/") and try to use Glib::build_filename()</code wherever possible.
  23. Use Glib for any file-system related activities (creating/removing/testing for files)
  24. Don't write: if (foo) delete foo; ... C++ handles delete (0); just fine, so just delete foo will do.
  25. include header files from a given "source" (e.g. libardour, system C headers, STL headers etc) in alphabetical order wherever possible.

Connecting and managing Signals

Ardour3 now uses boost::signals2 as its callback system. The following are some guidelines on how to ensure the best use of this API. The basic issue to pay attention to is that if an object makes a connection to a signal, something must be responsible for disconnecting the connection

  • If the object that creates the connection only makes 1 or 2 connections, add 1 or 2 boost::signals2::scoped_connection members to object's class, and assign the return value of the connect call to the relevant member. This ensures that when the object is deleted, the connections will be disconnected (thanks to the scoped_connection). Example: MIDI::MMC::mmc_connection or MIDI::Parser::trace_connection
       class Foo  {
         void method();
          boost::signals2::scoped_connection the_connection;

    boost::signals2::signal<void()> aSignal;

    Foo::Foo () {
    the_connection = aSignal.connect (boost::bind (&Foo::method, this));

  • If an object makes more than a couple of connections, it should inherit from PBD::ScopedConnectionList and used that class' scoped_connect() method to make all signal connections. This will also ensure that the connections are disconnected when the object is destroyed.
      #include "pbd/scoped_connections.h"
      class Foo : public PBD::ScopedConnectionList {
           Foo ();
           void a_method();

    boost::signals2::signal<void()> aSignal;

    Foo::Foo() {
    scoped_connect (aSignal, boost::bind (&Foo::method, this));

  • HOWEVER, if the object makes those connections and then breaks them again without being destroyed (e.g. an object that connects to a set of signals on another object, and drops those connections when told to use a different object), then add a PBD::ScopedConnectionList* member to the class. Initialize the pointer to zero; instantiate a new ScopedConnectionList before starting to make connections, and use the list's ::add_connection() method to add the return result of each signal::connect call. To drop all the connections, delete the list object.
      class Foo {
          Foo ();
      void connect (SomeObjectWithSignals&);  
      PBD::ScopedConnectionList* connections;


    Foo::Foo() : connections (0) {}
    Foo::~Foo() { delete connections; }

    void Foo::connect (SomeObjectWithSignals& obj) {
    delete connections;
    connections = new ScopedConnectionList;
    connections.add_connection (obj.aSignal, boost::bind (…));


  • Connections to static methods or regular C++ functions do not need to be scoped in these ways. Just connect to the signal normally.