Question

So, i’m writing some code in C for a larger program processing data for an ECG device. The program has several global int arrays to store data, as it has to continuously filter data, while also using both previous raw and filtered data. Therefore, i have to shift the ints in my arrays once in a while, in order to discard data that will no longer be used to filter and replace it with new raw data and so on. Implementing this is not more difficult than implementing some for loops here and there in my code that do this for me. I would however like to define a function that did this for me, as I do this quite a few times. Therefore I coded such a function, that looked like this:

void updateArray(int array[], int size){
size = size / sizeof(int);
int i;
for(i = size; i > 0; i--){
    array[i] = array[i-1];
}}

But, as I’m not that used to code in C, i have clearly done something wrong here, as using this function yielded wrong data. Debugging the function, I found that when this function is called, the array is shifted as expected, but one of my other arrays has one of its values changed. I’m not really sure why this is, but I really hope some feedback could help me understand the problem better.

Answer 1

array[size] is beyond the end of your array. You are copying one too many values.

It should be:

void updateArray(int array[], int size) {
    size = size / sizeof(int);
    int i;
    for(i = size - 1; i > 0; i--) {
        array[i] = array[i-1];
    }
}