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.. title:: clang-tidy - performance-inefficient-vector-operation
performance-inefficient-vector-operation
========================================
Finds possible inefficient ``std::vector`` operations (e.g. ``push_back``,
``emplace_back``) that may cause unnecessary memory reallocations.
It can also find calls that add element to protobuf repeated field in a loop
without calling Reserve() before the loop. Calling Reserve() first can avoid
unnecessary memory reallocations.
Currently, the check only detects following kinds of loops with a single
statement body:
* Counter-based for loops start with 0:
.. code-block:: c++
std::vector<int> v;
for (int i = 0; i < n; ++i) {
v.push_back(n);
// This will trigger the warning since the push_back may cause multiple
// memory reallocations in v. This can be avoid by inserting a 'reserve(n)'
// statement before the for statement.
}
SomeProto p;
for (int i = 0; i < n; ++i) {
p.add_xxx(n);
// This will trigger the warning since the add_xxx may cause multiple memory
// reallocations. This can be avoid by inserting a
// 'p.mutable_xxx().Reserve(n)' statement before the for statement.
}
* For-range loops like ``for (range-declaration : range_expression)``, the type
of ``range_expression`` can be ``std::vector``, ``std::array``,
``std::deque``, ``std::set``, ``std::unordered_set``, ``std::map``,
``std::unordered_set``:
.. code-block:: c++
std::vector<int> data;
std::vector<int> v;
for (auto element : data) {
v.push_back(element);
// This will trigger the warning since the 'push_back' may cause multiple
// memory reallocations in v. This can be avoid by inserting a
// 'reserve(data.size())' statement before the for statement.
}
Options
-------
.. option:: VectorLikeClasses
Semicolon-separated list of names of vector-like classes. By default only
``::std::vector`` is considered.
.. option:: EnableProto
When `true`, the check will also warn on inefficient operations for proto
repeated fields. Otherwise, the check only warns on inefficient vector
operations. Default is `false`.
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