std::size, std::ssize

#include <cassert>
#include <cstring>
#include <iostream>
#include <vector>
 
int main()
{
 // Works with containers
 std::vector <int> v{3, 1, 4};
 assert (std::size(v) == 3);
 
 // And works with built-in arrays too
 int a[]{-5, 10, 15};
 // Returns the number of elements (not bytes) as opposed to sizeof
 assert (std::size(a) == 3);
 std::cout << "size of a[]: " << sizeof a << '\n'; // 12, if sizeof(int) == 4
 
 // Provides a safe way (compared to sizeof) of getting string buffer size
 const char str[] = "12345";
 // These are fine and give the correct result
 assert (std::size(str) == 6);
 assert (sizeof(str) == 6);
 
 // But use of sizeof here is a common source of bugs
 const char* str_decayed = "12345";
 // std::cout << std::size(str_decayed) << '\n'; // Usefully fails to compile
 std::cout << sizeof(str_decayed) << '\n'; // Prints the size of the pointer!
 
 // Since C++20 the signed size (std::ssize) is available
 auto i = std::ssize(v);
 for (--i; i != -1; --i)
 std::cout << v[i] << (i ? ' ' : '\n');
 assert (i == -1);
 
 // Note that the string literal includes the ending null character, which
 // will be part of the constructed characters array. This makes std::size
 // behave differently from std::strlen and std::string::size:
 constexpr char symbols[] = "0123456789";
 
 static_assert(std::size(symbols) == 11);
 static_assert(std::string (symbols).size() == 10);
 assert (std::strlen (symbols) == 10);
}

size of a[]: 12
8
4 1 3