Vector Library

<vector>


A vector<T> is like an array of T, but supports copying, assignment, and comparison. Its size can be set and changed at run time, and it can efficiently implement a stack (O(1) time to push or pop). It has random iterators like string, which behave like type T* (or const T* if the vector is const). If T is numeric, elements are initialized to 0. It is not possible to have an initialization list such as {1,2,3}. vector<T>() // Empty vector, elements of type T
vector<T>(n) // n elements, default initialized
vector<T>(n, x) // n elements each initialized to x
vector<T> v2=v; // Copy v to v2
v2=v; // Assignment
v2<v // Also >, ==, !=, <=, >= if defined for T
vector<T>(b, e) // Initialize to sequence [b, e)
v.size() // n
vector<T>::size_type // Type of v.size(), usually unsigned int
v.empty() // true if v.size() == 0
v[i] // i'th element, 0 <= i < v.size() (unchecked), may be assigned to
v.at(i) // v[i] with bounds check, throws out_of_range
v.begin(), v.end() // Iterators [b, e)
vector<T>::iterator // Iterator type, also const_iterator
v.back() // v[v.size()-1] (unchecked if empty)
v.push_back(x) // Increase size by 1, copy x to last element
v.pop_back() // Decrease size by 1 (unchecked if empty)
v.front() // v[0] (unchecked)
v.resize(n) // Change size to n >= 0 (unchecked)
v.insert(d, x) // Insert x in front of iterator d, shift, increase size by 1
v.insert(d, n, x) // Insert n copies of x in front of d
v.insert(d, b, e) // Insert copy of [b, e) in front of d
v.erase(d) // Remove *d, shift, decrease size by 1
v.erase(d, e) // Remove subsequence [d, e)
v.clear() // v.erase(v.begin(), v.end())
v.reserve(n) // Anticipate that v will grow to size n >= v.size()
v.capacity() // Reserved size
For insert and erase, d and e must point into v (and d <= e) or the program may crash. Elements from *d to the end are shifted and the size is changed as needed. Saved copies of iterators may become invalid after any change of size or capacity (not checked).
To implement push_back() efficiently, a vector typically doubles the reserved space when it runs out in order to minimize memory reallocation and copying. reserve() allows this strategy to be optimized.
// Read words from input into a stack, print in reverse order
string s;
vector<string> v;
while (cin >> s)
v.push_back(s);
while (!v.empty()) {
cout << v.back() << endl;
v.pop_back();
}