How to memcpy a part of a two dimensional array in C?

Question

How to memcpy the two dimensional array in C:

I have a two dimensional array:

int a[100][100];

int c[10][10];

I want to use memcpy to copy the all the values in array c to array a, how to do this using memcpy?

int i;
for(i = 0; i<10; i++)
{
    memcpy(&a[i][10], c, sizeof(c));
}

is this correct?

That depends on where you want the values to go. It looks like not quite what you probably want. — Daniel Fischer
– Daniel Fischer, Commented Jun 3, 2013 at 12:00
You have 100 times the capacity in a. Which elements of a do you want to hold a copy of c? — simonc
– simonc, Commented Jun 3, 2013 at 12:00

Fabien · Accepted Answer · 2013-06-03 12:01:21Z

13

That should work :

int i;
for(i = 0; i<10; i++)
{
    memcpy(&a[i], &c[i], sizeof(c[0]));
}

answered Jun 3, 2013 at 12:01

Fabien

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Comments

cgledezma · Accepted Answer · 2013-06-03 12:02:49Z

3

It should actually be:

for(i = 0; i < 10; ++ i)
{
  memcpy(&(a[i][0]), &(c[i][0]), 10 * sizeof(int));
}

answered Jun 3, 2013 at 12:02

cgledezma

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2 Comments

user2131316 Over a year ago

when I try to do &(c[i][0]), it tells me that error: no match for 'operator[]' in '*(c+ 924u)[0]'

cgledezma Over a year ago

You sure you typed it right? My compiler tells me nothing.. Which compiler are you using?

unwind · Accepted Answer · 2013-06-03 12:00:49Z

1

I don't think it's correct, no.

There's no way for memcpy() to know about the in-memory layout of a and "respect" it, it will overwrite sizeof c adjacent bytes which might not be what you mean.

If you want to copy into a "sub-square" of a, then you must do so manually.

answered Jun 3, 2013 at 12:00

unwind

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