blob: 6a2c6876622a6bf80bbda5e70bff7e1af792a2c8 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
|
# reserve-candidates
Finds places that could use a `reserve()` call.
Whenever you know how many elements a container will hold you should reserve
space in order to avoid repeated memory allocations.
#### Trivial example missing reserve()
QList<int> ages;
// list.reserve(people.size());
for (auto person : people)
list << person.age();
Example where reserve shouldn't be used:
QLost<int> list;
for (int i = 0; i < 1000; ++i) {
// reserve() will be called 1000 times, meaning 1000 allocations
// whilst without a reserve the internal exponential growth algorithm would do a better job
list.reserve(list.size() + 2);
for (int j = 0; j < 2; ++j) {
list << m;
}
}
#### Supported containers
`QVector`, `std::vector`, `QList`, `QSet` and `QVarLengthArray`
#### Pitfalls
Rate of false-positives is around 15%. Don't go blindly calling `reserve()` without proper analysis.
In doubt don't use it, all containers have a growth curve and usually only do log(N) allocations
when you append N items.
|
