Move pointer in arrays with C

Question

Is there anyway I can move the pointer in the array. So, like you move where the pointer is pointing at in the array. For files, I know that you can use fseek with something like fread to only copy from a specific location.

I'm trying to copy parts of an array into different files. With fwrite, it doesn't give the option to start from a specific location, so I'll need to move the pointer to somewhere in the array, then copy a part of the array into a file.

You can use &array[index] to get a pointer to an element of the array. — Barmar
– Barmar, Commented Oct 6, 2020 at 1:11

pm100 · Accepted Answer · 2020-10-06 01:14:05Z

4

sure you can move a pointer. Say we have an array of ints

int arr[50];

set p to point at the first element

int*p = &arr[0];

now move it along by 10

p += 10;

p now points at arr[10];

Addition on a pointer is defined as incrementing the pointer by n times the size of each elements. Subtraction works too. Be aware of going off either end though, C wont look out for you. Ie this

p += 500;

will compile but will lead to undefined behavior if you try to use p;

answered Oct 6, 2020 at 1:14

pm100

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4 Comments

tenderporkk Over a year ago

Ok, thanks. I didn't realize that you could use & to receive the pointer to an element of an array. That makes lots of sense.

pm100 Over a year ago

@AlexZhao you can do int*p=&arr[10]

tenderporkk Over a year ago

Yes, except that I can keep incrementing to keep pointing to different elements of the array. Ok, thanks.

S F Over a year ago

@pm100 Actually, you can just write int*p = arr; instead of int*p = &arr[0];

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