C++ std::array Element access
Example
1. at(pos)
Returns a reference to the element at position pos with bounds checking. If pos is not within the range of the container, an exception of type std::out_of_range is thrown.
The complexity is constant O(1).
#include <array>
int main()
{
std::array<int, 3> arr;
// write values
arr.at(0) = 2;
arr.at(1) = 4;
arr.at(2) = 6;
// read values
int a = arr.at(0); // a is now 2
int b = arr.at(1); // b is now 4
int c = arr.at(2); // c is now 6
return 0;
}
2) operator[pos]
Returns a reference to the element at position pos without bounds checking. If pos is not within the range of the container, a runtime segmentation violation error can occur. This method provides element access equivalent to classic arrays and thereof more efficient than at(pos).
The complexity is constant O(1).
#include <array>
int main()
{
std::array<int, 3> arr;
// write values
arr[0] = 2;
arr[1] = 4;
arr[2] = 6;
// read values
int a = arr[0]; // a is now 2
int b = arr[1]; // b is now 4
int c = arr[2]; // c is now 6
return 0;
}
3) std::get<pos>
This non-member function returns a reference to the element at compile-time constant position pos without bounds checking. If pos is not within the range of the container, a runtime segmentation violation error can occur.
The complexity is constant O(1).
#include <array>
int main()
{
std::array<int, 3> arr;
// write values
std::get<0>(arr) = 2;
std::get<1>(arr) = 4;
std::get<2>(arr) = 6;
// read values
int a = std::get<0>(arr); // a is now 2
int b = std::get<1>(arr); // b is now 4
int c = std::get<2>(arr); // c is now 6
return 0;
}
4) front()
Returns a reference to the first element in container. Calling front() on an empty container is undefined.
The complexity is constant O(1).
Note: For a container c, the expression c.front() is equivalent to *c.begin().
#include <array>
int main()
{
std::array<int, 3> arr{ 2, 4, 6 };
int a = arr.front(); // a is now 2
return 0;
}
5) back()
Returns reference to the last element in the container.
Calling back() on an empty container is undefined.
The complexity is constant O(1).
#include <array>
int main()
{
std::array<int, 3> arr{ 2, 4, 6 };
int a = arr.back(); // a is now 6
return 0;
}
6) data()
Returns pointer to the underlying array serving as element storage. The pointer is such that range [data(); data() + size()) is always a valid range, even if the container is empty (data() is not dereferenceable in that case).
The complexity is constant O(1).
#include <iostream>
#include <cstring>
#include <array>
int main ()
{
const char* cstr = "Test string";
std::array<char, 12> arr;
std::memcpy(arr.data(), cstr, 12); // copy cstr to arr
std::cout << arr.data(); // outputs: Test string
return 0;
}
