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: 
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_expressioncan be- std::vector,- std::array,- std::deque,- std::set,- std::unordered_set,- std::map,- std::unordered_set:
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¶
- VectorLikeClasses¶
- Semicolon-separated list of names of vector-like classes. By default only - ::std::vectoris considered.
- 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.