还有TR1/ c++ 11/ c++ 17方式(参见Coliru Live):

const std::string s[3] = { "1"s, "2"s, "3"s };
constexpr auto n       = std::extent<   decltype(s) >::value; // From <type_traits>
constexpr auto n2      = std::extent_v< decltype(s) >;        // C++17 shorthand

const auto     a    = std::array{ "1"s, "2"s, "3"s };   // C++17 class template arg deduction -- http://en.cppreference.com/w/cpp/language/class_template_argument_deduction
constexpr auto size = std::tuple_size_v< decltype(a) >;

std::cout << n << " " << n2 << " " << size << "\n"; // Prints 3 3 3

#include <iostream>

int main ()
{
    using namespace std;
    int arr[] = {2, 7, 1, 111};
    auto array_length = end(arr) - begin(arr);
    cout << "Length of array: " << array_length << endl;
}

执行sizeof myArray将得到分配给该数组的总字节数。然后，您可以通过除以数组中一个元素的大小来找出数组中的元素数量:sizeof myArray[0]

所以，你会得到这样的东西:

size_t LengthOfArray = sizeof myArray / sizeof myArray[0];

由于sizeof产生size_t，结果LengthOfArray也将是这种类型。

对于旧的g++编译器，您可以这样做

template <class T, size_t N>
char (&helper(T (&)[N]))[N];

#define arraysize(array) (sizeof(helper(array)))

int main() {
    int a[10];
    std::cout << arraysize(a) << std::endl;
    return 0;
}

从c++ 11开始，引入了一些新的模板来帮助减少处理数组长度时的痛苦。它们都定义在header <type_traits>中。

std::rank<T>::value If T is an array type, provides the member constant value equal to the number of dimensions of the array. For any other type, value is 0. std::extent<T, N>::value If T is an array type, provides the member constant value equal to the number of elements along the Nth dimension of the array, if N is in [0, std::rank<T>::value). For any other type, or if T is array of unknown bound along its first dimension and N is 0, value is 0. std::remove_extent<T>::type If T is an array of some type X, provides the member typedef type equal to X, otherwise type is T. Note that if T is a multidimensional array, only the first dimension is removed. std::remove_all_extents<T>::type If T is a multidimensional array of some type X, provides the member typedef type equal to X, otherwise type is T.

要获得多维数组的任何维度上的长度，可以使用decltype与std::extent结合使用。例如:

#include <iostream>
#include <type_traits> // std::remove_extent std::remove_all_extents std::rank std::extent

template<class T, size_t N>
constexpr size_t length(T(&)[N]) { return N; }

template<class T, size_t N>
constexpr size_t length2(T(&arr)[N]) { return sizeof(arr) / sizeof(*arr); }

int main()
{
    int a[5][4][3]{{{1,2,3}, {4,5,6}}, { }, {{7,8,9}}};

    // New way
    constexpr auto l1 = std::extent<decltype(a)>::value;     // 5
    constexpr auto l2 = std::extent<decltype(a), 1>::value;  // 4
    constexpr auto l3 = std::extent<decltype(a), 2>::value;  // 3
    constexpr auto l4 = std::extent<decltype(a), 3>::value;  // 0

    // Mixed way
    constexpr auto la = length(a);
    //constexpr auto lpa = length(*a);  // compile error
    //auto lpa = length(*a);  // get at runtime
    std::remove_extent<decltype(a)>::type pa;  // get at compile time
    //std::remove_reference<decltype(*a)>::type pa;  // same as above
    constexpr auto lpa = length(pa);
    std::cout << la << ' ' << lpa << '\n';

    // Old way
    constexpr auto la2 = sizeof(a) / sizeof(*a);
    constexpr auto lpa2 = sizeof(*a) / sizeof(**a);
    std::cout << la2 << ' ' << lpa2 << '\n';

    return 0;
}

BTY，获取多维数组中元素的总数:

constexpr auto l = sizeof(a) / sizeof(std::remove_all_extents<decltype(a)>::type);

或者把它放在一个函数模板中:

#include <iostream>
#include <type_traits>
    

template<class T>
constexpr size_t len(T &a)
{
    return sizeof(a) / sizeof(typename std::remove_all_extents<T>::type);
}

int main()
{
    int a[5][4][3]{{{1,2,3}, {4,5,6}}, { }, {{7,8,9}}};
    constexpr auto ttt = len(a);
    int i;
    std::cout << ttt << ' ' << len(i) << '\n';
    
    return 0;
}

更多如何使用它们的例子可以通过以下链接找到。

对于c++ /CX(在Visual Studio中使用c++编写UWP应用程序时)，我们可以通过简单地使用size()函数来查找数组中值的数量。

源代码:

string myArray[] = { "Example1", "Example2", "Example3", "Example4" };
int size_of_array=size(myArray);

如果你计算size_of_array的输出将是:

>>> 4