Vectors#

pw_containers: Generic collections of objects for embedded devices

A vector is a one-dimensional array with a variable length. Pigweed’s vector type differs from the standard library in that it is backed by a fixed-size buffer.

pw::Vector#

Vectors must be declared with an explicit maximum size (e.g. Vector<int, 10>) but vectors can be used and referred to without the max size template parameter (e.g. Vector<int>).

To allow referring to a pw::Vector without an explicit maximum size, all Vector classes inherit from the generic Vector<T>, which stores the maximum size in a variable. This allows Vectors to be used without having to know their maximum size at compile time. It also keeps code size small since function implementations are shared for all maximum sizes.

Example#

 1class Publisher {
 2 public:
 3  using Subscriber = pw::Function<void(const Message&)>;
 4  static constexpr size_t kMaxSubscribers = 10;
 5
 6  pw::Status Subscribe(Subscriber&& subscriber) {
 7    // Check if the vector's fixed capacity has been exhausted.
 8    if (subscribers_.full()) {
 9      return pw::Status::ResourceExhausted();
10    }
11
12    // Add the subscriber to the vector.
13    subscribers_.emplace_back(std::move(subscriber));
14    return pw::OkStatus();
15  }
16
17  void Publish(const Message& message) {
18    // Iterate over the vector.
19    for (auto& subscriber : subscribers_) {
20      subscriber(message);
21    }
22  }
23
24 private:
25  pw::Vector<Subscriber, kMaxSubscribers> subscribers_;
26};

API reference#

The Vector class is similar to std::vector, except it is backed by a fixed-size buffer.

template<typename T, size_t kMaxSize = vector_impl::kGeneric>
class Vector : public pw::VectorStorage<T, vector_impl::kGeneric, std::is_trivially_destructible_v<T>>#

Size report#

The tables below illustrate the following scenarios:

  • The memory and code size cost incurred by a adding a single Vector.

  • The memory and code size cost incurred by adding another Vector with the same type as the first scenario, but with a different size. As Vector is templated on both type and size, a different size results in additional code being generated.

  • The memory and code size cost incurred by adding another Vector with the same size as the first scenario, but with a different type. As Vector is templated on both type and size, a different size results in additional code being generated.

Note

The size report that is usually displayed here is temporarily unavailable while we migrate the pigweed.dev build system from GN to Bazel. See b/388905812 for updates.

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