c++ - Declaring arrays with const variables -


i trying create multidimensional array, when pass const int value can't compile. error "expression must have constant value" each dimension.

class matrix {   public:      matrix(int rowcount, int columncount, int scalarinput) {           const int row_c = rowcount;         const int colum_c = columncount;         const int scalar_c = scalarinput;          matrixcalculation(row_c, colum_c, scalar_c);     }       void matrixcalculation(const int i, const int j, const int s) {          int matrixarray[i][j]; // error here, , j: "expression must have constant value"       }  };

thanks

array dimensions must compile-time constant, , const doesn't mean that.

a const object cannot change value after initialisation, initialiser may determined @ runtime (e.g. const int x = rand()) so, in general, these objects not valid candidates array dimensions.

introducing... constexpr.

if plonk keyword constexpr in front of dimensions, off start. compiler prevent breaking contract of constexpr, , consequently enable use shiny new constexpr object array dimension.

alas, in example, are breaking contract already, since inputs non-constant. tough cookies.

use vector instead.


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