如何获得三维数组的尺寸？

Question

我很高兴在C++11中发现我们可以用"auto“分配多个维度，但是我得到了定义"auto a=new float1030”和“float a11030”的奇怪的维度值。请帮助检查和任何可能的解决方案。

=============a.cpp =========================

#include <stdio.h>
#include <string.h>
#include <iostream>

template<class T>
size_t size(T const & a ) {  return sizeof a / sizeof (a[0]);}

int main(){
auto  a=new float[10][20][30];
float a1[10][20][30];
std::cout<<size(a)<<" "<<size(a[0])<<"  "<<size(a[0][0])<<"\n";
std::cout<<size(a1)<<" "<<size(a1[0])<<"  "<<size(a1[0][0])<<"\n";
delete[] a;
}

==========result========================

XUs mini:桌面徐$ g++ -std=c++11 a.cpp -o a XUs迷你:桌面徐$a 0 20 30 10 - 20 30

Answer 1

您可以使用模板执行如下操作：

#include <iostream>

template <typename T, size_t c0, size_t c1, size_t c2>
static size_t countof_0(const T (&arr)[c0][c1][c2]) {
    return c0;
}

template <typename T, size_t c0, size_t c1, size_t c2>
static size_t countof_1(const T (&arr)[c0][c1][c2]) {
    return c1;
}

template <typename T, size_t c0, size_t c1, size_t c2>
static size_t countof_2(const T (&arr)[c0][c1][c2]) {
    return c2;
}

int main() {
    double my_3d_array[21][11][32];

    std::cout << countof_0(my_3d_array) << "\n";
    std::cout << countof_1(my_3d_array) << "\n";
    std::cout << countof_2(my_3d_array) << "\n";
}

如果你能使函数成为常数，那么你应该。

Answer 2

下面是基于Chiris以上想法的代码，到5维，虽然很好：

        #include <stdio.h>
        #include <string.h>


        //-----------------------------------------------------------------
        //Get Dimension from 5D array
        //-----------------------------------------------------------------
        template <typename T, size_t c0, size_t c1, size_t c2,size_t c3,size_t c4>
        static size_t size1(const T (&arr)[c0][c1][c2][c3][c4]) {
            return c0;
        }
        template <typename T, size_t c0, size_t c1, size_t c2,size_t c3,size_t c4>
        static size_t size2(const T (&arr)[c0][c1][c2][c3][c4]) {
            return c1;
        }
        template <typename T, size_t c0, size_t c1, size_t c2,size_t c3,size_t c4>
        static size_t size3(const T (&arr)[c0][c1][c2][c3][c4]) {
            return c2;
        }
        template <typename T, size_t c0, size_t c1, size_t c2,size_t c3,size_t c4>
        static size_t size4(const T (&arr)[c0][c1][c2][c3][c4]) {
            return c3;
        }
        template <typename T, size_t c0, size_t c1, size_t c2,size_t c3,size_t c4>
        static size_t size5(const T (&arr)[c0][c1][c2][c3][c4]) {
            return c4;
        }
        //-----------------------------------------------------------------
        //Get Dimension from 4D array
        //-----------------------------------------------------------------
        template <typename T, size_t c0, size_t c1, size_t c2,size_t c3>
        static size_t size1(const T (&arr)[c0][c1][c2][c3]) {
            return c0;
        }
        template <typename T, size_t c0, size_t c1, size_t c2,size_t c3>
        static size_t size2(const T (&arr)[c0][c1][c2][c3]) {
            return c1;
        }
        template <typename T, size_t c0, size_t c1, size_t c2,size_t c3>
        static size_t size3(const T (&arr)[c0][c1][c2][c3]) {
            return c2;
        }
        template <typename T, size_t c0, size_t c1, size_t c2,size_t c3>
        static size_t size4(const T (&arr)[c0][c1][c2][c3]) {
            return c3;
        }

        //-----------------------------------------------------------------
        //Get Dimension from 3D array
        //-----------------------------------------------------------------
        template <typename T, size_t c0, size_t c1, size_t c2>
        static size_t size1(const T (&arr)[c0][c1][c2]) {
            return c0;
        }
        template <typename T, size_t c0, size_t c1, size_t c2>
        static size_t size2(const T (&arr)[c0][c1][c2]) {
            return c1;
        }
        template <typename T, size_t c0, size_t c1, size_t c2>
        static size_t size3(const T (&arr)[c0][c1][c2]) {
            return c2;
        }

        //-----------------------------------------------------------------
        //Get Dimension from 2D array
        //-----------------------------------------------------------------
        template <typename T, size_t c0, size_t c1>
        static size_t size1(const T (&arr)[c0][c1]) {
            return c0;
        }
        template <typename T, size_t c0, size_t c1>
        static size_t size2(const T (&arr)[c0][c1] ) {
            return c1;
        }

        //-----------------------------------------------------------------
        //Get Dimension from 1D array
        //-----------------------------------------------------------------
        template <typename T, size_t c0>
        static size_t size1(const T (&arr)[c0]) {
            return c0;
        }


        /*
        int main() {
            float my_3d_array[11][22][33][44] ;

            cout << size1(my_3d_array) << "\n";
            cout << size2(my_3d_array) << "\n";
            cout << size3(my_3d_array) << "\n";
            cout << size4(my_3d_array) << "\n";    
        }*/