public member function
<vector>
std::vector::capacity
size_type capacity() const;
size_type capacity() const noexcept;
Return size of allocated storage capacity
Returns the size of the storage space currently allocated for the vector, expressed in terms of elements.
This capacity is not necessarily equal to the vector size. It can be equal or greater, with the extra space allowing to accommodate for growth without the need to reallocate on each insertion.
Notice that this capacity does not suppose a limit on the size of the vector. When this capacity is exhausted and more is needed, it is automatically expanded by the container (reallocating it storage space). The theoretical limit on the size of a vector is given by member max_size.
The capacity of a vector can be explicitly altered by calling member vector::reserve.
Return Value
The size of the currently allocated storage capacity in the vector, measured in terms of the number elements it can hold.
Member type size_type is an unsigned integral type.
Example
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// comparing size, capacity and max_size
#include <iostream>
#include <vector>
int main ()
{
std::vector<int> myvector;
// set some content in the vector:
for (int i=0; i<100; i++) myvector.push_back(i);
std::cout << "size: " << (int) myvector.size() << '\n';
std::cout << "capacity: " << (int) myvector.capacity() << '\n';
std::cout << "max_size: " << (int) myvector.max_size() << '\n';
return 0;
}
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A possible output for this program could be:
size: 100
capacity: 128
max_size: 1073741823
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Iterator validity
No changes.
Data races
The container is accessed.
No contained elements are accessed: concurrently accessing or modifying them is safe.
Exception safety
No-throw guarantee: this member function never throws exceptions.