std::vector::data(3)

NAME
std::vector::data - std::vector::data

Synopsis
   T* data(); (1) (noexcept since C++11)
                        (constexpr since C++20)
   const T* data() const; (2) (noexcept since C++11)
                        (constexpr since C++20)
   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).

Parameters
   (none)

Return value
   Pointer to the underlying element storage. For non-empty containers, the returned
   pointer compares equal to the address of the first element.

Complexity
   Constant.

Notes
   If size() is 0, data() may or may not return a null pointer.

Example
// Run this code
 #include <cstddef>
 #include <iostream>
 #include <span>
 #include <vector>
 void pointer_func(const int* p, std::size_t size)
 {
     std::cout << "data = ";
     for (std::size_t i = 0; i < size; ++i)
         std::cout << p[i] << ' ';
     std::cout << '\n';
 }
 void span_func(std::span<const int> data) // since C++20
 {
     std::cout << "data = ";
     for (const int e : data)
         std::cout << e << ' ';
     std::cout << '\n';
 }
 int main()
 {
     std::vector<int> container{1, 2, 3, 4};
     // Prefer container.data() over &container[0]
     pointer_func(container.data(), container.size());
     // std::span (C++20) is a safer alternative to separated pointer/size.
     span_func({container.data(), container.size()});
 }

Output:
 data = 1 2 3 4
 data = 1 2 3 4
  Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 464 C++98 vector did not have this member added
                       function
   LWG 1312 C++98 the return type were pointer and changed to T* and const T*
                       const_pointer respectively

See also
   front access the first element
           (public member function)
   back access the last element
           (public member function)
   size returns the number of elements
           (public member function)
   span a non-owning view over a contiguous sequence of objects
   (C++20) (class template)
   data obtains the pointer to the underlying array
   (C++17) (function template)