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What is the difference between size() and max_size() functions for std: :array in C++?

  array<int,5> arr{ 1, 2, 3, 4, 5 }; 
  cout << arr.size(); 
  /* Output : 5 */ 
  
 array<int, 5> arr{ 1, 2, 3, 4, 5 }; 
 cout << arr.max_size(); 
 /* Output : 5 */
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    size and max_size are part of "interface" of most containers. For fixed sized std::array, there are indeed the same; for std::vector, there would be different. Commented Sep 23, 2021 at 12:24

2 Answers 2

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What is the difference between size() and max_size() functions for std: :array in C++?

The latter has prefix max_. There is no other practical difference between them for std::array.

The difference is conceptual. size is the current number of elements in the container, and max_size is a theoretical upper bound to how many elements the container could have. Since the number of elements in std::array is constant, the current number of elements is exactly the same as the number of elements there can ever be. For other containers, there is a practical difference.

Using the max_size member function of std::array is conceptually silly. It exists so that std::array conforms to the Container concept (e.g. named requirement), which allows it to be used uniformly with other containers, which is useful within templates.

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i think max_size() refers to the capacity of the array and not the actual size of the array.

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while arrays are similar to other containers by having a max_size they don't have capacity.
Furthermore, in case of a container that does have a capacity such as std::vector, std::vector::max_size has no correllaction with std::vector::capacity.

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