Using memcpy method

Question

I m looking for how to write a function like memcpy. Method that copy integers or chars from one array to other. What i mean, its to use memcpy, without using it. But in my case it does not work.

void Memcpy( void *from, void *to, int dimension, int length ) {

   if(dimension == sizeof(char)){
      char *copyFrom = (char *)from;
      char *copyTo = (char *)to;

      for(int i = length; i < length; i++)
         copyTo[i] = copyFrom[i];
   }


   if(dimension == sizeof(int)){
      int *copyFrom = (int *)from;
      int *copyTo = (int *)to;

      for(int i = length; i < length; i++)
         copyTo[i] = copyFrom[i];
   }
}

{Thank you for help =)}

Welcome to SO. You forgot to mention where you are stuck. What exactly is your problem? Show us your current effort for your copy function and we can help fixing the problem. — Gerhardh, Apr 11 '18 at 11:07
Have you already read https://codereview.stackexchange.com/questions/41094/memcpy-implementation and https://stackoverflow.com/questions/17591624/understanding-the-source-code-of-memcpy ? — Bob__, Apr 11 '18 at 13:36
Bob__, thank you very much. It was what I wanted to find!!!! — John J, Apr 11 '18 at 13:54

score 5 · Accepted Answer · answered Apr 11 '18 at 11:09

5

void copyOfArray( void *from, void *to, int dimension, int length ) {
     memcpy(to, from, dimension * length);
}

answered Apr 11 '18 at 11:09

Petar Velev

2,305
12
24

score 0 · Answer 2 · answered Apr 11 '18 at 11:29

What you want is really achieved with memcpy, there is no need to reinvent it. For your convinience you can wrap it with copy_of_array or even wrap copy_of_array with copy2 (as long as arrays are staticaly allocated).

#include <string.h>
#include <stdio.h>

#define copy2(src, dst, count, shift) copy_of_array(src, dst, count, sizeof(src[0]), shift)

copy_of_array (void * src,
               void * dst,
               int    count,
               int    elem_size,
               int    shift)
{
  memcpy (dst, (char*)src + elem_size * shift, count * elem_size);
}

int main() {
  int i;
  int ione[4] = { 1, 2, 3, 4};
  int itwo[2] = { 0, 0 };
  char cone[4] = { 'a', 'b', 'c', 'd'};
  char ctwo[2] = { 'x', 'y' };
  copy_of_array(ione, itwo, 1, sizeof(int), 3);
  for (i=0; i<2; i++ )
    printf("%d ", itwo[i] );

  copy2(cone, ctwo, 1, 3);
  for (i=0; i<2; i++ )
    printf("%c ", ctwo[i] );
}

Using memcpy method

2 Answers2