Passing an array as an argument to a function in C

c arrays function parameters parameter-passing
Mohan Mahajan picture Mohan Mahajan · Jul 4, 2011 · Viewed 191.4k times · Source

I wrote a function containing array as argument, and call it by passing value of array as follows.

void arraytest(int a[])
{
    // changed the array a
    a[0]=a[0]+a[1];
    a[1]=a[0]-a[1];
    a[0]=a[0]-a[1];
}

void main()
{
    int arr[]={1,2};
    printf("%d \t %d",arr[0],arr[1]);
    arraytest(arr);
    printf("\n After calling fun arr contains: %d\t %d",arr[0],arr[1]);
}

What I found is though I am calling arraytest() function by passing values, the original copy of int arr[] is changed.

Can you please explain why?

Answer

Bo Persson picture Bo Persson · Jul 4, 2011

When passing an array as a parameter, this

void arraytest(int a[])

means exactly the same as

void arraytest(int *a)

so you are modifying the values in main.

For historical reasons, arrays are not first class citizens and cannot be passed by value.

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