How to using movememory function?

Question

Hi,
I have a 5x2 matrix like this:
I want to remove the 3rd row (3 3) so I use the following code:

1 2
3 2
3 3
1 2
2 3


int colcount=2;
X* begin_ = begin()+2*colcount; //(pointer to 3- row3th )
...
MoveMemory(begin_ + colcount, begin_, (5-3) * colcount) * sizeof(X));
this->row-=1;

+ 5-3 is the number rows of block to move

However I get unexpected results.
Maybe I'm misinterpreting? this is my first time using this function.
How to fix this?

Thank you

Answer 1

I think you will find the documentation at multidimensional-arrays-c helpful to understand how the addresses of array rows and elements are determined.

And an example -

#define WIN32_LEAN_AND_MEAN  
#include <Windows.h>  
  
#include <stdio.h>  
#include <stdlib.h>  
  
int main()  
{  
    int aInts[5][2] = {  
        {1,2},  
        {3,4},  
        {5,6},  
        {7,8},  
        {9,10}  
    };  
  
    int Rows = _countof(aInts);  
    int Cols = _countof(aInts[0]);  
  
    printf("Before move\n");  
    for (int r = 0; r < Rows; ++r)  
        for (int c = 0; c < Cols; ++c)  
            printf("aInts[%d][%d] = %d\n", r, c, aInts[r][c]);  
  
    int* dest = aInts[2]; // address of row 3  
    int* source = aInts[3]; // address of row 4  
    SIZE_T cBytes = 2 * sizeof(int[2]); // number of rows * size of a row  
    MoveMemory(dest, source, cBytes);  
  
    printf("\nAfter move overwriting row 3\n");  
    for (int r = 0; r < Rows; ++r)  
        for (int c = 0; c < Cols; ++c)  
            printf("aInts[%d][%d] = %d\n", r, c, aInts[r][c]);  
  
    return 0;  
}