memcpy with startIndex?

Question

I wish to copy content of specific length from one buffer to another from a specific starting point. I checked memcpy() but it takes only the length of content

Answer 1

I always prefer the syntax

memcpy( &dst[dstIdx], &src[srcIdx], numElementsToCopy * sizeof( Element ) );

Answer 2

You could have a function like below.

template<typename T>
T* memcopy_index(T* dst,T* src,unsigned int index, unsigned int element_count)
{
    return (T*)memcpy(dst,src + index, element_count * sizeof(T));
}

It can be used as below:

int src[]={0,1,2,3,4,5,6};
int dst[15];

memcopy_index(dst,src,2,5);    //copy 5 elements from index 2

You have to make sure that destination buffer has enough room to copy the elements.

Answer 3

Just add the offset you want to the address of the buffer.

char abuff[100], bbuff[100];
....
memcpy( bbuff, abuff + 5, 10 );

This copies 10 bytes starting at abuff[5] to bbuff.