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1.. title:: clang-tidy - readability-enum-initial-value2 3readability-enum-initial-value4==============================5 6Enforces consistent style for enumerators' initialization, covering three7styles: none, first only, or all initialized explicitly.8 9An inconsistent style and strictness to defining the initializing value of10enumerators may cause issues if the enumeration is extended with new11enumerators that obtain their integer representation implicitly.12 13The following three cases are accepted:14 15#. **No** enumerators are explicit initialized.16#. Exactly **the first** enumerator is explicit initialized.17#. **All** enumerators are explicit initialized.18 19.. code-block:: c++20 21 enum A { // (1) Valid, none of enumerators are initialized.22 a0,23 a1,24 a2,25 };26 27 enum B { // (2) Valid, the first enumerator is initialized.28 b0 = 0,29 b1,30 b2,31 };32 33 enum C { // (3) Valid, all of enumerators are initialized.34 c0 = 0,35 c1 = 1,36 c2 = 2,37 };38 39 enum D { // Invalid, d1 is not explicitly initialized!40 d0 = 0,41 d1,42 d2 = 2,43 };44 45 enum E { // Invalid, e1, e3, and e5 are not explicitly initialized.46 e0 = 0,47 e1,48 e2 = 2,49 e3, // Dangerous, as the numeric values of e3 and e5 are both 3, and this is not explicitly visible in the code!50 e4 = 2,51 e5,52 };53 54This check corresponds to the CERT C Coding Standard recommendation `INT09-C. Ensure enumeration constants map to unique values55<https://wiki.sei.cmu.edu/confluence/display/c/INT09-C.+Ensure+enumeration+constants+map+to+unique+values>`_.56 57`cert-int09-c` redirects here as an alias of this check.58 59Options60-------61 62.. option:: AllowExplicitZeroFirstInitialValue63 64 If set to `false`, the first enumerator must not be explicitly initialized to65 a literal ``0``.66 Default is `true`.67 68 .. code-block:: c++69 70 enum F {71 f0 = 0, // Not allowed if AllowExplicitZeroFirstInitialValue is false.72 f1,73 f2,74 };75 76 77.. option:: AllowExplicitSequentialInitialValues78 79 If set to `false`, explicit initialization to sequential values are not80 allowed.81 Default is `true`.82 83 .. code-block:: c++84 85 enum G {86 g0 = 1, // Not allowed if AllowExplicitSequentialInitialValues is false.87 g1 = 2,88 g2 = 3,89