readability-enum-initial-value

Enforces consistent style for enumerators’ initialization, covering three styles: none, first only, or all initialized explicitly.

An inconsistent style and strictness to defining the initializing value of enumerators may cause issues if the enumeration is extended with new enumerators that obtain their integer representation implicitly.

The following three cases are accepted:

1. No enumerators are explicit initialized.

2. Exactly the first enumerator is explicit initialized.

3. All enumerators are explicit initialized.

enum A {    // (1) Valid, none of enumerators are initialized.
  a0,
  a1,
  a2,
};

enum B {    // (2) Valid, the first enumerator is initialized.
  b0 = 0,
  b1,
  b2,
};

enum C {    // (3) Valid, all of enumerators are initialized.
  c0 = 0,
  c1 = 1,
  c2 = 2,
};

enum D {    // Invalid, d1 is not explicitly initialized!
  d0 = 0,
  d1,
  d2 = 2,
};

enum E {    // Invalid, e1, e3, and e5 are not explicitly initialized.
  e0 = 0,
  e1,
  e2 = 2,
  e3,       // Dangerous, as the numeric values of e3 and e5 are both 3, and this is not explicitly visible in the code!
  e4 = 2,
  e5,
};

This check corresponds to the CERT C Coding Standard recommendation INT09-C. Ensure enumeration constants map to unique values.

cert-int09-c redirects here as an alias of this check.

Options

AllowExplicitZeroFirstInitialValue

If set to false, the first enumerator must not be explicitly initialized to a literal 0. Default is true.

enum F {
  f0 = 0, // Not allowed if AllowExplicitZeroFirstInitialValue is false.
  f1,
  f2,
};

AllowExplicitSequentialInitialValues

If set to false, explicit initialization to sequential values are not allowed. Default is true.

enum G {
  g0 = 1, // Not allowed if AllowExplicitSequentialInitialValues is false.
  g1 = 2,
  g2 = 3,