C++ vector reserve() Function
Example
Reserve memory for 100 numbers:
vector<int> numbers;
numbers.reserve(100);
cout << "Size: " << numbers.size() << "\n";
cout << "Room for 100 numbers: " << (numbers.capacity() >= 100 ? "Yes" : "No");Definition and Usage
The reserve() function reserves memory for a number of elements, so that the capacity is at least that number. If the capacity is already large enough, nothing happens.
It does not add any elements, so the size does not change. If you know how many elements you will add, reserve() can make the program faster, because the vector does not need to reserve new memory many times.
The reserve function is defined in the <vector> header file.
Syntax
vector.reserve(size_t amount);The size_t data type is a non-negative integer.
Parameter Values
| Parameter | Description |
|---|---|
| amount | Required. The number of elements to reserve memory for. |
Technical Details
| Returns: | Nothing (void). |
|---|
Related Pages
Read more about vectors in our Vector Tutorial.
