Finding array length

Posted on 2004-08-04
Last Modified: 2011-08-18

I am currently getting frustrated about a problem I have been thinking about for ages.

If I have a function:

void in_array_cp(char *haystack[],char *needle)

which is supposed to find out if an array (haystack) contains a certain element(needle), I need to know the number of elements in the array to be able to scan through it. Is there a way to find the number of elements in the array or do I need to pass it as another parameter?

by the way: I am using GCC3.3.1 on SuSE Linux9
Question by:Professor
LVL 46

Expert Comment

by:Sjef Bosman
ID: 11713153
1. No way
2. Yes, you need another parameter to pass the # of elements.
LVL 45

Accepted Solution

sunnycoder earned 125 total points
ID: 11713162
Hi Professor,

> Is there a way to find the number of elements in the array or do I need to pass it as another
> parameter?

Number of valid elements -> pass another parameter
Array capacity -> if actually declared as array then sizeof(array)/sizeof(element)
               -> if declared as pointer and malloced then again pass another argument

LVL 16

Expert Comment

ID: 11713172
Yes, but only if you make some assumptions.

You could assume that the las entry in the haystack is NULL.

You could assume a fixed number of entries in haystack.

You could assume that haystack has been allocated on-heap.

I cant think of any other reliable way to tell without making assumptions.

The required code should be obvious for each of the above assumptions but if you need help, just ask.

Good luck.


Expert Comment

ID: 14811679
Yes, as PaulCaswell  says, keeping a NULL at the end of your haystack[]  seems to be a better idea to me. this will allow you to determine the length of array by keep counting the number of elements until a NULL occurs.

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