Can't read values of array in C

Question

const char reset = '3';
char savedArray[32] = "0000000000000000000000000000000";
savedArray[reset] = '1';
Serial.println(savedArray[reset]);
Serial.println(savedArray[3]);
Serial.println(savedArray);

So I am changing the value of the savedArray at position 3, but when I read it out again I find it 0.. What am I doing wrong? Why isn't reset the same as 3?

Serial output:

1
0
0000000000000000000000000000000

use saveArray[32] = {0}; instead of savedArray[32] = 0000000000000000000000000000000"; — msc
– msc, Commented Sep 19, 2016 at 7:54
@MathewsMathai It should be size_t reset, if we wanted to nitpick. — Andrea Biondo
– Andrea Biondo, Commented Sep 19, 2016 at 8:10
@MathewsMathai No, it was me nitpicking :) char and int will work (because 3 fits), size_t would be the choice for generic indexing. — Andrea Biondo
– Andrea Biondo, Commented Sep 19, 2016 at 8:38

Bathsheba · Accepted Answer · 2016-09-19 07:56:03Z

4

Assuming ASCII or even EBCDIC encoding '3' is a value larger than 32. (In ASCII, it's 51).

The behaviour on using this in savedArray[reset] is undefined since you are attempting to access an index outside the bounds of the array savedArray. Use const char reset = 3; to assign the numeric value of 3 to any numeric type, including const char.

answered Sep 19, 2016 at 7:56

Bathsheba

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Comments

David Ranieri · Accepted Answer · 2016-09-19 07:55:34Z

3

No, you are changing the array element 51 (the value of '3' in the ASCII table), so you are accessing outside of the bounds of the array.

Change to const char reset = 3;

answered Sep 19, 2016 at 7:55

David Ranieri

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Comments

Sourav Ghosh · Accepted Answer · 2016-09-19 08:17:23Z

2

So I am changing the value of the savedArray at position 3.

Wait, there you went wrong. You're not at all changing the value at position 3. In your code,

const char reset = '3';

is the same as

const char reset = 51;  //considering ASCII

because, character literal (constant)'3' represents decimal 51 (in ACSII) and for which , later

savedArray[reset] = '1';

is out of bound access, as savedArray is of size 32. You might want to write

 const char reset = 3;  //decimal 3

or,

#define RESET 3  //MACROS are better suited as "array index", just suggesting

edited Sep 19, 2016 at 8:17

answered Sep 19, 2016 at 7:56

Sourav Ghosh

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