# std::vector<T,Allocator>::shrink_to_fit

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< cpp‎ | container‎ | vector

void shrink_to_fit(); |  | (since C++11) (until C++20)
constexpr void shrink_to_fit(); |  | (since C++20)

Requests the removal of unused capacity.

It is a non-binding request to reduce capacity() to size(). It depends on the implementation whether the request is fulfilled.

If new size() is greater than capacity() the function causes reallocation, in which case all iterators (including the end() iterator) and all references to the elements are invalidated. If no reallocation takes place, no iterators or references are invalidated.

### Parameters

(none)

Type requirements
- `T` must meet the requirements of MoveInsertable.

### Return value

(none)

### Complexity

At most linear in the size of the container.

### Notes

If an exception is thrown other than by T's move constructor, there are no effects.

### 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

### See also

size | returns the number of elements (public member function)
capacity | returns the number of elements that can be held in currently allocated storage (public member function)

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