std::vector at() method

since C++20

// prism-push-types:reference,const_reference,size_type
// Non const version
constexpr reference       at( size_type pos );

// Const version
constexpr const_reference at( size_type pos ) const;

until C++20

// prism-push-types:reference,const_reference,size_type
// Non const version
reference       at( size_type pos );

// Const version
const_reference at( size_type pos ) const;

Returns a reference

to the element at specified index pos.

Bounds checking is performed.

Parameters

• pos - position of the element to return

Return value

Reference to the requested element.

Exceptions

Throws std::out_of_range if pos >= size().

Complexity

Constant - O(1).

Example

Main.cpp

#include <iostream>
#include <vector>
 
int main()
{
	std::vector<int> data = { 1, 2, 4, 5, 5, 6 };

	// Set element 1
	data.at(1) = 88;

	// Read element 2
	std::cout << "Element at index 2 has value " << data.at(2) << '\n';

	std::cout << "data size = " << data.size() << '\n';

	try {
		// Set element 6
		data.at(6) = 666;
	} catch (std::out_of_range const& exc) {
		std::cout << exc.what() << '\n';
	}

	// Print final values
	std::cout << "data:";
	for (int elem : data)
		std::cout << " " << elem;
	std::cout << '\n';
}

Possible output

Element at index 2 has value 4
data size = 6
vector::_M_range_check: __n (which is 6) >= this->size() (which is 6)
data: 1 88 4 5 5 6