## Integer array length

Integer array length
# 1
09-08-2013
Integer array length

Hello;
When I wrote a function to print out an array,
I could only print out the first two elements,( sometimes 8 out of 10 elements). What did I miss?
The problem seems to be the part My understanding is (copied from stackoverflow):
sizeof returns the size in memory of the passed element. By dividing the size of an array by a single element size, you get the elements count. On the other hand, when counting elements in an array: sizeof(a) / sizeof(a[0]) will still work as well.
But my code does not! I saw this type online quite lot, but mine just does not work (Ubuntu 12.10, 64_bits kernel). Could anyone explain what is wrong with my code? Thanks a lot!
 yifangt View Public Profile for yifangt Find all posts by yifangt
# 2
09-08-2013
Your array is passed as a pointer. There's no way for your function to know the size of the array, unless you pass that too.

i.e.
A 64-bit pointer (8 bytes) divided by an integer of 4 bytes = 2, which is why you're seeing only two elements.
This User Gave Thanks to Scott For This Post:
 Scott View Public Profile for Scott Find all posts by Scott
# 3
09-08-2013

i'll try your code on my machine once i'll get to home but i would rather like to do this by

Last edited by Scott; 09-08-2013 at 09:52 AM.. Reason: Code tags
 kg_gaurav View Public Profile for kg_gaurav Find all posts by kg_gaurav
# 4
09-08-2013
Quote:
Originally Posted by kg_gaurav
i'll try your code on my machine once i'll get to home but i would rather like to do this by

void p_array(int arr[])
{
int *a = arr;
// int size = sizeof (arr) / sizeof (arr[0]);
while(a!=NULL)
{ printf("%d ", *a);a++}

printf("\n");
}
You can't.
 achenle View Public Profile for achenle Find all posts by achenle
# 5
09-08-2013
Thanks everybody!
Scott, what I want is to let my function by itself get the size of the array, especially when the array size is unknown.
Your explanation about "2" is what I thought, but how come sometime it print 8 elements of the array?
I feel it is related to array and pointer/address, but I could not figure it out myself, especially when google gives many discussions, for example, this one. but I am still unclear the problem with my code. Thanks a lot again!
 yifangt View Public Profile for yifangt Find all posts by yifangt
# 6
09-08-2013
Quote:
Originally Posted by yifangt
Your explanation about "2" is what I thought, but how come sometime it print 8 elements of the array?
Show us the code that prints 8 elements. An entire program, not just the printing function. If it is an extremely long program, eliminate all non-essentials and construct a minimal case that still prints out 8 elements. Perhaps then, we can provide accurate feedback.

Given what you've shown us, I believe Scott's explanation is as good as it gets. For more info regarding his point, refer to the comp.lang.c FAQ - Question 6.4.

Regards,
Alister
 alister View Public Profile for alister Find all posts by alister
# 7
09-08-2013
Here is my code, which is for quick sort I am trying to understand each step of the algorithm.
I labeled the p_array call for convenience when you point out the problem. I could not understand in the main function line 10, which works fine, but not
line 66.
Output:
Why?
By the way, this is NOT an assignment from school, but my self-study. Appreciate any input. Thanks a lot!

Last edited by yifangt; 09-09-2013 at 12:49 AM.. Reason: improve the question
 yifangt View Public Profile for yifangt Find all posts by yifangt

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