C ++访问指向结构的指针中的类数组指针

Question

I am new to C++ and I really need some help on this. I am trying to create a structure to interface with the GSL Monte-Carlo algorithms (a fact that is really not important for this example). I have searched all of the C++ tutorials, the stackoverflow posts and the GSL documentation with no luck. I am using the armadillo package for matrix manipulation; it is very robust. I am unable to use a dynamic array within the structure, as per the documentation, so I am trying to find a way to make my structure variable *M point to the values in my array *L[]. I am sure that this would be better with a vector but 1) the rest of the code (in bad form) uses pointers already, and 2) I am looking at this as a learning experience. I am surprised that the addresses for *M and *L[] are not the same in my code. I am also, less importantly, surprised that my std::cout prints a different number of spaces for each line. The code exits before printing the last std::cout as shown in the output below.

Thanks for your help!

#include "pch.h"
#include "stdio.h"
#include "complex"
#include "new"
#include "armadillo"
using namespace arma;

class Link
{
public:

    arma::Mat<cx_double>::fixed<3, 3>* dir[4];                                      // pointer to directional SU(3) matrices

    Link();                                                                         // default constructor

};

Link::Link()                                                                        // default constructor - all directional matrices are the identity 
{

    for (size_t hcount = 0; hcount < 4; hcount++)
    {
        dir[hcount] = new arma::Mat<cx_double>::fixed<3, 3>{ fill::eye };           // create directional matrix in direction hcount
    }

}

struct Param
{
    Link* M;
};

int main()
{
    const int size  = 10;
    Param* Parameters = new Param{ NULL };
    Link* L[size];
    arma::Mat<cx_double>::fixed<3, 3> One{ fill::eye };


    for (size_t hcount = 0; hcount < 10; hcount++)
    {
        L[hcount] = new Link();
        *L[hcount]->dir[1] = *L[hcount]->dir[1] + hcount * One;                     // Make each array element #1 unique
    }

    Parameters->M = L[0];

    std::cout << "&L                        = " << &L << std::endl;
    std::cout << "&Parameters->M            = " << &Parameters->M << std::endl;                 // surprised that addresses are not the same
    std::cout << std::endl;

    std::cout << "&L[0]                     = " << &L[0] << std::endl;
    std::cout << "&Parameters->M[0]         = " << &Parameters->M[0] << std::endl;
    std::cout <<  std::endl;

    std::cout << "&L[5]                     = " << &L[5] << std::endl;
    std::cout << "&Parameters->M[5]         = " << &Parameters->M[5] << std::endl;
    std::cout << std::endl;

    std::cout << "&L[5]->dir[1]             = " << &L[5]->dir[1] << std::endl;
    std::cout << "&Parameters->M[5].dir[1]  = " << &Parameters->M[5].dir[1] << std::endl;
    std::cout << std::endl;

    std::cout << "*L[5]->dir[1]             = " << *L[5]->dir[1] << std::endl;                  // This works
    std::cout << "*Parameters->M[5].dir[1]  = " << *Parameters->M[5].dir[1] << std::endl;       // This does not
    std::cout << std::endl;

}

OUTPUT
&L                                              = 0024F7CC
&Parameters->M                  = 004EEFD8

&L[0]                                           = 0024F7CC
&Parameters->M[0]                       = 004E0578

&L[5]                                           = 0024F7E0
&Parameters->M[5]                       = 004E05C8

&L[5]->dir[1]                           = 004E50C4
&Parameters->M[5].dir[1]        = 004E05CC

*L[5]->dir[1]                           =     (+6.000e+00,+0.000e+00)                      (0,0)                      (0,0)
                      (0,0)    (+6.000e+00,+0.000e+00)                      (0,0)
                      (0,0)                      (0,0)    (+6.000e+00,+0.000e+00)

*Parameters->M[5].dir[1]        = 

Answer 1

&L is the adress of L , so it's the adress of the pointer to the first element not the adress of the first elemenr itself. Same for & Parameters->M . That is the adress of thd the Member M from Parameters . You want to compare L[0] with Parameters->M except when M should not point to the element that L[0] refers to but to the start of the array itself, then you want to compare it with L . But then you also have to change the assignment.

I find it a bit weird that you use an array of pointers. Just use an array of Link s.