Buffer.BlockCopy vs Array.Copy

  • Thread starter Thread starter Jono
  • Start date Start date
J

Jono

Hi Everyone,
I've read the documentation on MSDN regarding Buffer's methods being
faster than Array's for primitive types. So I gave it a try, but it
doesn't copy all the data I ask it to (it stops after 7 items). I have
a C# code sample, where I create an array with 32k items, and set the
value of each item to its index in the array... then I use both
Buffer.BlockCopy and Array.Copy to copy the first 25 items into a sub
array:


<code>
int[] source = new int[short.MaxValue];
for (int index = 0; index < source.Length; index++)
{
source[index] = index;
}
int count = 25;

int[] bufferBlockCopy = new int[count];
Buffer.BlockCopy(source, 0, bufferBlockCopy, 0,
count);
Print(bufferBlockCopy);

int[] arrayCopy = new int[count];
Array.Copy(source, 0, arrayCopy, 0, count);
Print(arrayCopy);
</code>

bufferBlockCopy has zeros after index 7, while arrayCopy has all the
correct indexes.

Have I fundamentally misunderstood the usage pattern of
Buffer.BlockCopy or is there some kind of bug in the framework (or my
test) code?

Many thanks,

Jono
 
Jono said:
Hi Everyone,
I've read the documentation on MSDN regarding Buffer's methods being
faster than Array's for primitive types. So I gave it a try, but it
doesn't copy all the data I ask it to (it stops after 7 items). I have
a C# code sample, where I create an array with 32k items, and set the
value of each item to its index in the array... then I use both
Buffer.BlockCopy and Array.Copy to copy the first 25 items into a sub
array:


<code>
int[] source = new int[short.MaxValue];
for (int index = 0; index < source.Length; index++)
{
source[index] = index;
}
int count = 25;

int[] bufferBlockCopy = new int[count];
Buffer.BlockCopy(source, 0, bufferBlockCopy, 0,
count);
Print(bufferBlockCopy);

int[] arrayCopy = new int[count];
Array.Copy(source, 0, arrayCopy, 0, count);
Print(arrayCopy);
</code>

bufferBlockCopy has zeros after index 7, while arrayCopy has all the
correct indexes.

Have I fundamentally misunderstood the usage pattern of
Buffer.BlockCopy or is there some kind of bug in the framework (or my
test) code?

Many thanks,

Jono
Click to expand...

Hi,

BlockCopy expects the number of bytes to copy, not the number of elements.

-Zsolt
 
Hi Everyone,
I've read the documentation on MSDN regarding Buffer's methods being
faster than Array's for primitive types. So I gave it a try, but it
doesn't copy all the data I ask it to (it stops after 7 items). I have
a C# code sample, where I create an array with 32k items, and set the
value of each item to its index in the array... then I use both
Buffer.BlockCopy and Array.Copy to copy the first 25 items into a sub
array:
Click to expand...
<code>
               int[] source = new int[short.MaxValue];
               for (int index = 0; index < source.Length; index++)
               {
                   source[index] = index;
               }
               int count = 25;
Click to expand...
               int[] bufferBlockCopy = new int[count];
               Buffer.BlockCopy(source, 0, bufferBlockCopy, 0,
count);
               Print(bufferBlockCopy);
Click to expand...
               int[] arrayCopy = new int[count];
               Array.Copy(source, 0, arrayCopy, 0, count);
               Print(arrayCopy);
</code>
Click to expand...
bufferBlockCopy has zeros after index 7, while arrayCopy has all the
correct indexes.
Click to expand...
Have I fundamentally misunderstood the usage pattern of
Buffer.BlockCopy or is there some kind of bug in the framework (or my
test) code?
Click to expand...
Many thanks,
Click to expand...
Jono
Click to expand...

Hi,

BlockCopy expects the number of bytes to copy, not the number of elements..

-Zsolt
Click to expand...

Haha! Brilliant. Thank you for letting me know so quickly. Regards,
Jono
 
Back
Top