sorting dynamic array of structures with STL algorithm sort

I am having problem with sorting a dynamic allocated array of struct, please help me find out what goes wrong.

Here's my code

#include <iostream>
#include <algorithm>
#include <cstdio>
using namespace std;

struct Box{
    int *dimval;
    int dim;

    ~Box(){
        delete[] dimval;
    }

    friend bool operator < (const Box& a, const Box& b){
        for(int i=0; i<a.dim;i++){
            if(a.dimval[i]>b.dimval[i])
                return false;
        }
        return true;
    }

    void msort(){
        sort(dimval, dimval+dim);
    }

} *boxes;

int main(){
    int num_box, dim;

    scanf("%d%d", &num_box, &dim);

    boxes = new Box[num_box];
    for(int i=0;i<num_box;i++){
        boxes[i].dim = dim;
        boxes[i].dimval = new int[dim];
    }

    for(int i=0;i<num_box; i++){
            for(int j=0;j<dim; j++){
                scanf("%d", &(boxes[i].dimval[j]));
            }
            boxes[i].msort();
    }

    for(int i=0;i<num_box; i++){
            for(int j=0;j<dim; j++){
                cout<<boxes[i].dimval[j]<<" ";
            }
            cout<<endl;
    }
    cout<<"-----"<<endl;

    sort(boxes, boxes+num_box);
    for(int i=0;i<num_box; i++){
        for(int j=0;j<dim; j++){
            cout<<boxes[i].dimval[j]<<" ";
        }
        cout<<endl;
    }
    cout<<"xxxxxxx"<<endl;
}

Given the sample input

8 6
5 2 20 1 30 10
23 15 7 9 11 3
40 50 34 24 14 4
9 10 11 12 13 14
31 4 18 8 27 17
44 32 13 19 41 19
1 2 3 4 5 6
80 37 47 18 21 9

The output for the above code snippet is

1 2 5 10 20 30 
3 7 9 11 15 23 
4 14 24 34 40 50 
9 10 11 12 13 14 
4 8 17 18 27 31 
13 19 19 32 41 44 
1 2 3 4 5 6 
9 18 21 37 47 80 
-----
1 2 3 4 5 6 
1 2 5 10 20 30 
201056 200608 9 11 15 23 
4 14 24 34 40 50 
9 10 11 12 13 14 
4 8 17 18 27 31 
201728 200784 19 32 41 44 
9 18 21 37 47 80 
xxxxxxx

As you can see, sorting inside a Box struct is good, but sorting among Box is troublesome, can anyone help explain the problem here and how should it be resolved. Thanks

----------------------UPDATE---------------------------------------

I know using pointer to box might be the devil, but I cannot see why, please enlighten me with reasons and examples. Besides, the following is a code snippet from a sample solution. Here, the only difference is that it's using an array of struct instead of a pointer to a dynamically allocated array, and it's getting the correct output

here's the code

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
using namespace std;

struct Node{
    int A[12];
    int k;
    void Sort(){
        sort(A,A+k);
    }
    friend bool operator < (const Node&a, const Node&b){
        for(int i=0; i<a.k; ++i){
            if(a.A[i]>b.A[i])return false;
        }
        return true;
    }
}arr[32];

int n,k;

int main(){
scanf("%d%d",&n,&k);
       for(int i=0; i<n; ++i){
            for(int j=0; j<k; ++j)
                scanf("%d",&arr[i].A[j]);
            arr[i].k=k;
            arr[i].Sort();
        }
        for(int i=0;i<n; i++){
            for(int j=0;j<k; j++){
                cout<<arr[i].A[j]<<" ";
            }
            cout<<endl;
        }
        cout<<"-----"<<endl;

        sort(arr,arr+n);
        for(int i=0;i<n; i++){
            for(int j=0;j<k; j++){
                cout<<arr[i].A[j]<<" ";
            }
            cout<<endl;
        }
        cout<<"xxxxxx"<<endl;
}

1 2 5 10 20 30 
3 7 9 11 15 23 
4 14 24 34 40 50 
9 10 11 12 13 14 
4 8 17 18 27 31 
13 19 19 32 41 44 
1 2 3 4 5 6 
9 18 21 37 47 80 
-----
1 2 3 4 5 6 
1 2 5 10 20 30 
3 7 9 11 15 23 
4 14 24 34 40 50 
9 10 11 12 13 14 
4 8 17 18 27 31 
13 19 19 32 41 44 
9 18 21 37 47 80 
xxxxxx

----------------------------UPDATE 2-----------------------

I tried to add a copy constructor and an assignment overload to my Box struct, but this didn't work out as expected. The error code is ntdll!RtlpNtEnumerateSubKey() at 0x779d0725
Anything wrong with this implementation?

struct Box{
    int *dimval;
    int no;
    int dim;

    Box(){};

    Box(const Box& another){
        no = another.no;
        dim = another.dim;
        dimval = new int[no];
        memcpy(dimval, another.dimval, dim*sizeof(int));
    }

    Box& operator = (const Box& another){
        if(this != &another){
            no = another.no;
            dim = another.dim;
            int* tmp = new int[no];
            delete [] dimval;
            dimval = tmp;
            memcpy(dimval, another.dimval, dim*sizeof(int));
        }
        return *this;
    }

    ~Box(){
        delete[] dimval;
    }

    friend bool operator < (const Box& a, const Box& b){
        for(int i=0; i<a.dim;i++){
            if(a.dimval[i]>=b.dimval[i])
                return false;
        }
        return true;
    }

    void msort(){
        sort(dimval, dimval+dim);
    }

} *boxes;