Ошибка c2131 выражение не определяется константой

I am trying to learn about const and constexpr and have run into the error C26498 on VS2019. However, my example is almost the same as described here:

constexpr int myInt();
constexpr int getMyValue();
void foo();

int main()
{
    int val1 = myInt(); // C26498 warning (mark variable constexpr)
    const int val2 = myInt();    // C26498 warning (mark variable constexpr)
    constexpr int val3 = myInt();  // C2131 error (expression did not evaluate to a constant)
    foo();
}

constexpr int myInt() { return 1; }

constexpr int getMyValue() { return 1; }

void foo() { constexpr int val0 = getMyValue(); // no C26498 }

Edit: As requested, here is the error list (VS2019):

Warning C26498 — The function ‘myInt’ is constexpr, mark variable ‘val1’
constexpr if compile-time evaluation is desired (con.5). line 13

Warning C26498 — The function ‘myInt’ is constexpr, mark variable ‘val2’
constexpr if compile-time evaluation is desired (con.5). line 14

Error C2131 — expression did not evaluate to a constant line 15

Message — failure was caused by call of undefined function or one not
declared ‘constexpr’ line 15

I do understand the warnings for val1 and val2, but then when I do use constexpr for val3, I get an error. Why does this throw an error when almost the same code, encapsulated in another function (foo()) doesn’t? From my (limited) understanding, can’t myInt() also be computed at compile time?

// foo.hpp file
class foo
{
public:
static const int nmConst;
int arr[nmConst]; // line 7
};
// foo.cpp file
const int foo::nmConst= 5;

Решение

class foo
{
public:

static const int nmConst = 10;
int arr[nmConst];

};

Другие решения

Других решений пока нет …

У меня есть ниже код:

Clustering::Clustering( VectorIntPtr locus_encoding ){
    // Allocate memory and initialise
    _cluster_assignment = allocate_VectorInt( PROBLEM->ndata() );
    for( int i=0; i<PROBLEM->ndata(); i++ ){ _cluster_assignment[ i ] = -1; }
    _total_clusters = 0; // Total number of clusters found  
    int previous[ PROBLEM->ndata() ];
    // Get assinment of each data element to a cluster
    // Each connected component of the graph (as encoded in the adjacency-base encoding)
    // represents a different cluster
    for( int i=0; i<PROBLEM->ndata(); i++ ){
        int ctr = 0; 
        // Unassigned element found, assign cluster
        if( _cluster_assignment[ i ] == -1 ){
            // Assign to cluster, keep track of it, 
            // and identify neighbour (adjacent element)
            _cluster_assignment[ i ] = _total_clusters;
            previous[ ctr++ ] = i;
            int neighbour = locus_encoding[ i ]; 
            // Repeat operation for consecutive neighboring elements
            // and assign to the same cluster
            while( _cluster_assignment[ neighbour ] == -1 ){
                _cluster_assignment[ neighbour ] = _total_clusters;
                previous[ ctr++ ] = neighbour;
                neighbour = locus_encoding[ neighbour ]; 
            }      
            // If a previously assigned neighbour is reached,
            // and this element was assigned to a different cluster X, 
            // re-assign all elements in 'previous' list to cluster X
            if( _cluster_assignment[ neighbour ] != _total_clusters ){
                while( --ctr >= 0 ){
                    _cluster_assignment[ previous[ ctr ] ] = _cluster_assignment[ neighbour ]; 
                }
            }else{
                // Increase cluster counter
                _total_clusters++;
            }
        }       
    }
    // Centroid computation
    compute_cluster_centres();
}

Но в этой строке int previous[ PROBLEM->ndata() ]; поймите меня ниже ошибка:

error C2131: expression did not evaluate to a constant

И, скажем, ошибка была вызвана непостоянными аргументами или ссылкой на непостоянный символ, и обратите внимание: см. Использование «ПРОБЛЕМА».

В моем A.hh я заявляю как ниже:

ClusteringProblemPtr PROBLEM;

И в mock_ClusteringProblem.fwd.hh это как mock_ClusteringProblem.fwd.hh ниже:

#ifndef __MOCK_CLUSTERINGPROBLEM_FWD_HH__
#define __MOCK_CLUSTERINGPROBLEM_FWD_HH__

class ClusteringProblem;
typedef ClusteringProblem * ClusteringProblemPtr;

#endif 

Что я могу сделать?

(Я использую из Microsoft Visual Studio 2017 — версия 15.9.6)