Iterate Through a C Array
I Have an Array of Structs That I Created Somewhere in My Program. Later, I Want to Iterate Through That, but I Don't Have the Size of the Array. How Can I...
I have an array of structs that I created somewhere in my program.
Later, I want to iterate through that, but I don't have the size of the array.
How can I iterate through the elements? Or do I need to store the size somewhere?
4 Answers
If the size of the array is known at compile time, you can use the structure size to determine the number of elements.
struct foo fooarr[10];
for(i = 0; i < sizeof(fooarr) / sizeof(struct foo); i++)
{
do_something(fooarr[i].data);
}
If it is not known at compile time, you will need to store a size somewhere or create a special terminator value at the end of the array.
You can store the size somewhere, or you can have a struct with a special value set that you use as a sentinel, the same way that \0 indicates the end of a string.
It depends. If it's a dynamically allocated array, that is, you created it calling malloc, then as others suggest you must either save the size of the array/number of elements somewhere or have a sentinel (a struct with a special value, that will be the last one).
If it's a static array, you can sizeof it's size/the size of one element. For example:
int array[10], array_size;
...
array_size = sizeof(array)/sizeof(int);
Note that, unless it's global, this only works in the scope where you initialized the array, because if you past it to another function it gets decayed to a pointer.
Hope it helps.
I think you should store the size somewhere.
The null-terminated-string kind of model for determining array length is a bad idea. For instance, getting the size of the array will be O(N) when it could very easily have been O(1) otherwise.
Having that said, a good solution might be glib's Arrays, they have the added advantage of expanding automatically if you need to add more items.
P.S. to be completely honest, I haven't used much of glib, but I think it's a (very) reputable library.
Maya is a hardware enthusiast who tests and reviews smart home devices, smartphones, wearables, and audio gear. She focuses on practical consumer value and build quality.
