Enumeration

Enums allow meaningful names to be used instead of magic numbers. The first enum has the value 0 with each subsequent enum incrementing by 1:

enum Status {
  Stopped,  // 0
  Running,  // 1
  Paused    // 2
};

Status status;
switch (status) {
  case Stopped: break;
  case Running: break;
  case Paused: break;
}

Enums can be assigned custom values. Enums that did not get assigned a custom value will be the previous enum's value plus one:

enum HttpStatus {
  OK = 200,
  NotFound = 404,
  InternalError = 500,
  NotImplemented  // 501
};

The enum's default underlying type is an int. This underlying type can be changed to any integral type that can represent all the enum values:

enum Status : char {
  Stopped = 'S',
  Running = 'R',
  Paused = 'P'
};

The enums covered so far are unscoped enums which pollutes the enclosing scope and can implicitly convert breaking type safety. Enums can be scoped by declaring enum class:

enum class Status {
  Stopped,
  Running,
  Paused
};

Status status;
switch (status) {
  case Status::Stopped: break;
  case Status::Running: break;
  case Status::Paused: break;
}

Implicit conversions from scoped enum values to integral types are not allowed:

// int s = status;                 // error
int s = static_cast<int>(status);  // ok

switch (status) {
  using enum Status;
  case Stopped: break;
  case Running: break;
  case Paused: break;
}