C++

Reference

<vector>

vector

public member function
<vector>

std::vector::front

      reference front();const_reference front() const;
Access first element
Returns a reference to the first element in the vector.

Unlike member vector::begin, which returns an iterator to this same element, this function returns a direct reference.

Calling this function on an empty container causes undefined behavior.

Parameters

none

Return value

A reference to the first element in the vector container.

If the vector object is const-qualified, the function returns a const_reference. Otherwise, it returns a reference.

Member types reference and const_reference are the reference types to the elements of the container (see vector member types).

Example

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// vector::front
#include <iostream>
#include <vector>

int main ()
{
  std::vector<int> myvector;

  myvector.push_back(78);
  myvector.push_back(16);

  // now front equals 78, and back 16

  myvector.front() -= myvector.back();

  std::cout << "myvector.front() is now " << myvector.front() << '\n';

  return 0;
}

Output:
myvector.front() is now 62


Complexity

Constant.

Iterator validity

No changes.

Data races

The container is accessed (neither the const nor the non-const versions modify the container).
The reference returned can be used to access or modify elements. Concurrently accessing or modifying different elements is safe.

Exception safety

If the container is not empty, the function never throws exceptions (no-throw guarantee).
Otherwise, it causes undefined behavior.

See also

vector::at
Access element (public member function)
vector::operator[]
Access element (public member function)
vector::back
Access last element (public member function)