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1.. title:: clang-tidy - bugprone-suspicious-enum-usage2 3bugprone-suspicious-enum-usage4==============================5 6The checker detects various cases when an enum is probably misused7(as a bitmask).8 91. When "ADD" or "bitwise OR" is used between two enum which come10 from different types and these types value ranges are not disjoint.11 12The following cases will be investigated only using :option:`StrictMode`. We13regard the enum as a (suspicious)14bitmask if the three conditions below are true at the same time:15 16* at most half of the elements of the enum are non pow-of-2 numbers (because of17 short enumerations)18* there is another non pow-of-2 number than the enum constant representing all19 choices (the result "bitwise OR" operation of all enum elements)20* enum type variable/enumconstant is used as an argument of a `+` or "bitwise21 OR" operator22 23So whenever the non pow-of-2 element is used as a bitmask element we diagnose a24misuse and give a warning.25 262. Investigating the right hand side of ``+=`` and ``|=`` operator.273. Check only the enum value side of a ``|`` and ``+`` operator if one of28 them is not enum val.294. Check both side of ``|`` or ``+`` operator where the enum values are from30 the same enum type.31 32Examples:33 34.. code-block:: c++35 36 enum { A, B, C };37 enum { D, E, F = 5 };38 enum { G = 10, H = 11, I = 12 };39 40 unsigned flag;41 flag =42 A |43 H; // OK, disjoint value intervals in the enum types ->probably good use.44 flag = B | F; // Warning, have common values so they are probably misused.45 46 // Case 2:47 enum Bitmask {48 A = 0,49 B = 1,50 C = 2,51 D = 4,52 E = 8,53 F = 16,54 G = 31 // OK, real bitmask.55 };56 57 enum Almostbitmask {58 AA = 0,59 BB = 1,60 CC = 2,61 DD = 4,62 EE = 8,63 FF = 16,64 GG // Problem, forgot to initialize.65 };66 67 unsigned flag = 0;68 flag |= E; // OK.69 flag |=70 EE; // Warning at the decl, and note that it was used here as a bitmask.71 72Options73-------74 75.. option:: StrictMode76 77 Default value: 0.78 When non-null the suspicious bitmask usage will be investigated additionally79 to the different enum usage check.80