public member function

std::vector::front

<vector> 
      reference front();
const_reference front() const;

      reference front() noexcept;
const_reference front() const noexcept;
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 deque 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 first element is potentially accessed or modified by the caller. Concurrently accessing or modifying other 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 )

C++