如何从方法返回一个静态const int std :: array?

我试图从一个函数返回一个常量的int std :: array,但是我遇到了错误而且我不知道如何修复它们 .

始终不应更改 refmatrix 中的这些值 . 's why I' m使用常量int .

reference.h

#include <array>
#include <iostream>

using namespace std;

class Reference {
public:
    static const size_t NCOLS = 3;
    static const size_t NBITS = 4;
    static const size_t NROWS = 4;

private:
    static array<array<array<const int, NBITS>, NCOLS>, NROWS> refmatrix;

public:
    Reference();
    ~Reference();

    array<const int, NBITS> smaller(int *arry);
};

reference.cpp

#include "reference.h"

array<array<array<const int, Reference::NBITS>, Reference::NCOLS>, Reference::NROWS> Reference::refmatrix = {{{{{0, 1, 2, 6}, {6, 4, 1, 7}, {6, 7, 8, 3}}}, 
                                                                                                              {{{7, 0, 5, 2}, {1, 6, 9, 3}, {1, 4, 8, 0}}}, 
                                                                                                              {{{9, 3, 4, 6}, {0, 7, 2, 8}, {5, 3, 9, 4}}}, 
                                                                                                              {{{8, 9, 1, 4}, {7, 2, 6, 0}, {4, 0, 3, 7}}}}};

Reference::Reference() {}
Reference::~Reference() {}

array<const int, Reference::NBITS> Reference::smaller(int *arry) {
    int j;

    for(int i=0; i < NROWS; i++){
        for(j=0; j < NCOLS; j++){
            if(refmatrix[i][0][j] != arry[j]){
                j = (NCOLS + 1);
            }
        }
        if(j == NCOLS){
            return refmatrix[i][1];
        }
    }
}

main.cpp中

#include "reference.h"

int main() {
    Reference r;
    int arr[3] = {0, 1, 2};
    array<const int, Reference::NBITS> resp;

    resp = r.smaller( arr );

    // After get these values I will write it in a file.

    return 0;
}
main.cpp: In function ‘int main()’:

main.cpp:6:37: error: use of deleted function ‘std::array<const int, 4>::array()’
  array<const int, Reference::NBITS> resp;
                                     ^~~~

In file included from reference.h:1:0,
                 from main.cpp:1:

/usr/include/c++/7.3.0/array:94:12: note: ‘std::array<const int, 4>::array()’ is implicitly deleted because the default definition would be ill-formed:
     struct array
            ^~~~~

/usr/include/c++/7.3.0/array:94:12: error: uninitialized const member in ‘struct std::array<const int, 4>’

/usr/include/c++/7.3.0/array:110:56: note: ‘const int std::array<const int, 4>::_M_elems [4]’ should be initialized
       typename _AT_Type::_Type                         _M_elems;
                                                        ^~~~~~~~

main.cpp:9:33: error: use of deleted function ‘std::array<const int, 4>& std::array<const int, 4>::operator=(std::array<const int, 4>&&)’
  resp = r.smaller( arr );
                                 ^

In file included from reference.h:1:0,
                 from main.cpp:1:

/usr/include/c++/7.3.0/array:94:12: note: ‘std::array<const int, 4>& std::array<const int, 4>::operator=(std::array<const int, 4>&&)’ is implicitly deleted because the default definition would be ill-formed:
     struct array
            ^~~~~

/usr/include/c++/7.3.0/array:94:12: error: non-static const member ‘const int std::array<const int, 4>::_M_elems [4]’, can’t use default assignment operator

回答(1)

2 years ago

该错误与返回 std::array 无关 . 它与分配给 const 有关 .

您需要使用调用初始化 resp ,而不是默认初始化然后分配 .

int main() {
    Reference r;
    int arr[3] = {0, 1, 2};
    array<const int, Reference::NBITS> resp = r.smaller( arr );

    // After get these values I will write it in a file.

    return 0;
}

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