Removing elements from an array in C

by

There are really two separate issues. The first is keeping the elements of the array in proper order so that there are no “holes” after removing an element. The second is actually resizing the array itself.

Arrays in C are allocated as a fixed number of contiguous elements. There is no way to actually remove the memory used by an individual element in the array but the elements can be shifted to fill the hole made by removing an element. For example:

void remove_element(array_type *array, int index, int array_length)
{
   int i;
   for(i = index; i < array_length - 1; i++) array[i] = array[i + 1];
}

Statically allocated arrays can not be resized. Dynamically allocated arrays can be resized with realloc(). This will potentially move the entire array to another location in memory, so all pointers to the array or to its elements will have to be updated. For example:

remove_element(array, index, array_length);  /* First shift the elements, then reallocate */
array_type *tmp = realloc(array, (array_length - 1) * sizeof(array_type) );
if (tmp == NULL && array_length > 1) {
   /* No memory available */
   exit(EXIT_FAILURE);
}
array_length = array_length - 1;
array = tmp;

realloc will return a NULL pointer if the requested size is 0, or if there is an error. Otherwise it returns a pointer to the reallocated array. The temporary pointer is used to detect errors when calling realloc because instead of exiting it is also possible to just leave the original array as it was. When realloc fails to reallocate an array it does not alter the original array.

Note that both of these operations will be fairly slow if the array is large or if a lot of elements are removed. There are other data structures like linked lists and hashes that can be used if efficient insertion and deletion is a priority.

More Related Contents:

  1. Is it possible to use notation [] with pointers in C?
  2. C array pointer increment
  3. I need help understanding this code in C [closed]
  4. C | Static array: why does writing out-of-bounds not result in exception? [duplicate]
  5. C-programming board game [duplicate]
  6. Is an array name a pointer?
  7. Getting a stack overflow exception when declaring a large array
  8. How do I work with dynamic multi-dimensional arrays in C?
  9. Using malloc for allocation of multi-dimensional arrays with different row lengths
  10. Exceptions to array decaying into a pointer?
  11. Why do arrays in C decay to pointers?
  12. What is the maximum size of an array in C?
  13. How does GCC implement variable-length arrays?
  14. Pointer address in a C multidimensional array
  15. No compiler error when fixed size char array is initialized without enough room for null terminator
  16. Performance of 2-dimensional array vs 1-dimensional array
  17. Malloc a 3-Dimensional array in C?
  18. initializing an array of ints
  19. Need help using qsort with an array of structs
  20. Changing array inside function in C
  21. dynamic allocating array of arrays in C
  22. How can I work with dynamically-allocated arbitrary-dimensional arrays?
  23. Why does scanf() need & operator (address-of) in some cases, and not others? [duplicate]
  24. What’s the difference between array and &array?
  25. Array of structs replacing values over itself
  26. Pointer expressions: **ptr++, *++*ptr and ++**ptr use
  27. How do you get the size of array that is passed into the function?
  28. Cast T[][] to T*
  29. Detecting mismatched array enum initializers
  30. How many chars can be in a char array?

Leave a Comment