std::vector<T,Allocator>::shrink_to_fit
From cppreference.com
void shrink_to_fit(); |
(constexpr since C++20) | |
Requests the removal of unused capacity.
It is a non-binding request to reduce capacity() to size()
If reallocation occurs, all iterators (including the end()
|
If |
(since C++11) |
Complexity
At most linear in the size of the container.
ExceptionsIf an exception is thrown other than by the move constructor of a non-CopyInsertable
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(since C++11) |
Notes
In libstdc++, shrink_to_fit() is not available in C++98 mode.
Example
Run this code
#include <iostream> #include <vector> int main() { std::vector<int> v; std::cout << "Default-constructed capacity is " << v.capacity() << '\n'; v.resize(100); std::cout << "Capacity of a 100-element vector is " << v.capacity() << '\n'; v.resize(50); std::cout << "Capacity after resize(50) is " << v.capacity() << '\n'; v.shrink_to_fit(); std::cout << "Capacity after shrink_to_fit() is " << v.capacity() << '\n'; v.clear(); std::cout << "Capacity after clear() is " << v.capacity() << '\n'; v.shrink_to_fit(); std::cout << "Capacity after shrink_to_fit() is " << v.capacity() << '\n'; for (int i = 1000; i < 1300; ++i) v.push_back(i); std::cout << "Capacity after adding 300 elements is " << v.capacity() << '\n'; v.shrink_to_fit(); std::cout << "Capacity after shrink_to_fit() is " << v.capacity() << '\n'; }
Possible output:
Default-constructed capacity is 0 Capacity of a 100-element vector is 100 Capacity after resize(50) is 100 Capacity after shrink_to_fit() is 50 Capacity after clear() is 50 Capacity after shrink_to_fit() is 0 Capacity after adding 300 elements is 512 Capacity after shrink_to_fit() is 300
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 755 | C++98 | std::vector lacked explicit shrink-to-fit operations
|
provided |
| LWG 2033 | C++98 C++11 |
1. the complexity requirement was missing (C++98) 2. T was not required to be MoveInsertable
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1. added 2. required |
| LWG 2223 | C++98 C++11 |
1. references, pointers, and iterators were not invalidated (C++98) 2. there was no exception safety guarantee (C++11) |
1. they may be invalidated 2. added |
See also
| returns the number of elements (public member function) |
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| returns the number of elements that can be held in currently allocated storage (public member function) |