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1.. title:: clang-tidy - performance-inefficient-vector-operation2 3performance-inefficient-vector-operation4========================================5 6Finds possible inefficient ``std::vector`` operations (e.g. ``push_back``,7``emplace_back``) that may cause unnecessary memory reallocations.8 9It can also find calls that add element to protobuf repeated field in a loop10without calling Reserve() before the loop. Calling Reserve() first can avoid11unnecessary memory reallocations.12 13Currently, the check only detects following kinds of loops with a single14statement body:15 16* Counter-based for loops start with 0:17 18.. code-block:: c++19 20 std::vector<int> v;21 for (int i = 0; i < n; ++i) {22 v.push_back(n);23 // This will trigger the warning since the push_back may cause multiple24 // memory reallocations in v. This can be avoid by inserting a 'reserve(n)'25 // statement before the for statement.26 }27 28 SomeProto p;29 for (int i = 0; i < n; ++i) {30 p.add_xxx(n);31 // This will trigger the warning since the add_xxx may cause multiple memory32 // reallocations. This can be avoid by inserting a33 // 'p.mutable_xxx().Reserve(n)' statement before the for statement.34 }35 36* For-range loops like ``for (range-declaration : range_expression)``, the type37 of ``range_expression`` can be ``std::vector``, ``std::array``,38 ``std::deque``, ``std::set``, ``std::unordered_set``, ``std::map``,39 ``std::unordered_set``:40 41.. code-block:: c++42 43 std::vector<int> data;44 std::vector<int> v;45 46 for (auto element : data) {47 v.push_back(element);48 // This will trigger the warning since the 'push_back' may cause multiple49 // memory reallocations in v. This can be avoid by inserting a50 // 'reserve(data.size())' statement before the for statement.51 }52 53 54Options55-------56 57.. option:: VectorLikeClasses58 59 Semicolon-separated list of names of vector-like classes. By default only60 ``::std::vector`` is considered.61 62.. option:: EnableProto63 64 When `true`, the check will also warn on inefficient operations for proto65 repeated fields. Otherwise, the check only warns on inefficient vector66 operations. Default is `false`.67