将数组的一部分作为函数参数传递

Question

I have an array int arr[5] = {10, 2, 3, 5, 1} , and I want to pass in the last 4 elements (basically from index 1 to index4) into an argument as an array (so: [2, 3, 5, 1] ). Is there a way to do this very simply (like how in Ruby you would be able to do arr[1..4]), or would I have to use a for loop?

Answer 1

You can manually increment the pointer by 1:

your_function(arr + 1)

Pointer arithmetic in C implicitly accounts for the size of the elements, so adding 1 will actually add 1 * sizeof(int)

For a closer analogue to array slicing from other languages, try this function:

int *slice_array(int *array, int start, int end) {
    int numElements = (end - start + 1)
    int numBytes = sizeof(int) * numElements;

    int *slice = malloc(numBytes);
    memcpy(slice, array + start, numBytes)

    return slice;
}

It makes a slice of the array between the given start and end indices. Remember to free() the slice once you're done with it!

Answer 2

Answer

Given you current code:

int arr[5] = {10, 2, 3, 5, 1};

You can duplicate the range 1..4 by:

int arr_dup[4];
memcpy(arr_dup,arr+1,sizeof(int)*4);

Remember that your function definition should be a pointer, example:

void a_function(int *arr_arg); //Call via a_function(arr_dup);

Explanation

Arrays in c implemented as pointers (aka variables that hold memory addresses).

If you do arithmetic on the pointer, it will advance to the respective element. Example:

ptr + 1 //Next Element
ptr - 1 //Previous Element

Answer 3

#include <stdio.h>
#include <stdlib.h>

void my_function(int arr_size, int *arr)
{
  int i;
  for(i=0; i < arr_size; i++)
    {
      printf("[%d]:%d\n", i, arr[i]);
    }
}

int main(int argc, char **argv)
{
  int arr[] = { 10, 2, 3, 5, 1 };
  (void)my_function(4, &arr[1]); /* TODO > use more flexible indexing */
  return EXIT_SUCCESS;
}

Answer 4

I think you can use memcpy , memcpy can copy data byte to byte.In memmory,our data is binary,so even int is 4 bytes,we can copy it byte to byte.

---

int dst[4];
memcpy(dst,&arr[1],size(int) * 4);