array[].length -Workarounds ?

Projects Programming
1

hi,
I am searching for some workarounds for array[].length.

How do you solve this problems? I think there are 3 of them:

1.) cycling through an array
2.) calculating with the length (arithmectic mean)
3.) check if some item is the last item

I found this:

int length(int array[])
{
  int len = sizeof(array)/sizeof(array[0])
  return len;
}

But this will work just for one type of arrays. Is there a way to write a function which works for every array. If multidemensional, if string-aray or anything?

Regards,
Kevin

2

But this will work just for one type of arrays

It won't work for any type of array. (except maybe arrays with one element)

What do you want to do?

3

Create an Array object that allocates space dynamically and stores the size.

4

What do you want to do?

I like using arrays and in my (planned) project I would like to use a lot of them, but without being able to determin the last item of an array I loose its main advantage as a list.

I would like to program some kind of schedule (I know there are some around, but they do not meet my requirements).

The schedule should be read from a SD-Card into an array during setup. In the loop I am referring to the array. I need to cycle through the rows, performing some checks and checking the following row. While in last row the following row should be the first.

So I need a foreach-function and a check for the last row in the array.

I think I might need to find a way saving all array-lengths in a separate array. For the multi-dimensional arrays this will get a bit confusing...

5

I like using arrays and in my (planned) project I would like to use a lot of them

Be aware that you might run out of RAM...

6

Right. This could become a problem. But as I have to loop (and check) very quick (lets say ~100ms) I avoided some calculations by generating some tables. Maybe I should redo this and check how long a loop will take...

7

With these multi-dimensional arrays an array of structures is often a better approach, with a global telling how many items in the array.

but without being able to determin the last item of an array I loose its main advantage as a list.

With structures you can have a "last item" flag but this is a bit wasteful when a single external variable will do the same.

Is there any reason not to have a item counter as a global var?

Rob

8

Three words. Standard Template Library.

I'm working on it. Results look good so far.

#include "vector.h"
#include <Streaming.h>

using namespace std;

void foo (vector<int> & z)
{
Serial << "items in array are " << z.size () << endl;
}

void setup () {
Serial.begin (115200);
 
vector<int> x (10);

for (byte a = 0; a < 10; a++)
  x [a] = a;
 
for (vector<int>::const_iterator i = x.begin (); i != x.end(); i++)
  Serial.println (*i);
  
Serial << "backwards!" << endl;

for (vector<int>::reverse_iterator i = x.rbegin (); i != x.rend(); i++)
  Serial.println (*i);

foo (x);
x.resize (20);
foo (x);
}

void loop () {}

Output:

0
1
2
3
4
5
6
7
8
9
backwards!
9
8
7
6
5
4
3
2
1
0
items in array are 10
items in array are 20

Arrays can be dynamically sized. You can determine the size of an array in a called function. Arrays can be traversed forwards and backwards. You can find the first item. The last item. And much much more.

9

The nice thing about the STL is that the arrays (vectors) can be of any type. Adding to the previous example:

Serial << "bytes" << endl;

vector<byte> w (5);

for (byte a = 0; a < 5; a++)
  w [a] = a * 2;

for (vector<byte>::const_iterator i = w.begin (); i != w.end(); i++)
  Serial.println (*i, DEC);

Now we have an array of bytes. Output:

bytes
0
2
4
6
8
10

And you can sort arrays:

sort (x.rbegin (), x.rend ());

for (vector<int>::const_iterator i = x.begin (); i != x.end(); i++)
  Serial.println (*i);

Output:

9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
0
11

I was under the impression that there was no STL support in avr-gcc? I may be mistaken, of course.

--edit--

Then again, I just found this on the internet. Of course, dynamic arrays are going to burn up available memory real fast.

12

I had looked at some length for an STL port that ran on the Arduino, without success. So thanks for that link. I was half-way through doing one myself.

However a quick test seems to show that his uses more program memory than what I have ported so far, so I might continue for a bit longer.

As for burning up memory, yes that is a concern. But if the application requires the array anyway, whether or not it is done with STL won't change much. In fact, without dynamic memory you tend to allocate a big array "just in case", and if you need a few, then you are allocating a lot of big arrays "just in case" and using a lot of memory anyway. The actual container takes 6 or 7 bytes of memory (to hold its pointers) so that is the only overhead over the data you need to have anyway.

Your link came out a bit strange (with quotes in it) so I'll re-post it: