Check array element for null

Question

I have an array called quint8 block[16] which I:

initialize to zero with block[16] = { 0 }
fill it with some data
then pass it to a method/function as an argument like this bool fill(const quint8 *data)

In this fill function I want to see if the array is filled completely or if it contains null elements that were not filled.

Is it correct to perform a check this way? if(!data[i])? I have seen similar Q&A on this forum but all of them use \0 or NULL and I've heard this is not a good style for doing so and that has confused me.

Is it correct to perform a check this way? if(!data[i])?: Yes it is, but IMHO is more readable as if(data[i] == 0). — Dimitrios Bouzas
– Dimitrios Bouzas, Commented Aug 11, 2014 at 22:07
@juanchopanza the problem is that i can have elements with 0 value and that's valid data. — max
– max, Commented Aug 11, 2014 at 22:08
@MoKi Yes, that could be a problem. But it doesn't change the fact that an array of integers cannot have null elements. — juanchopanza
– juanchopanza, Commented Aug 11, 2014 at 22:14

TheUndeadFish · Accepted Answer · 2014-08-11 22:43:58Z

4

Integer types do not have a "null" concept in C++.

Two possible ideas are:

1) Use some specific integer value to mean "not set". If 0 is valid for your data, then obviously it cannot be used for this. Maybe some other value would work, such as the maximum for the type (which looks like it would be 0xff in this case). But if all possible values are valid for your data, then this idea won't work.

2) Use some other piece of data to track which values have been set. One way would be an array of bools, each corresponding to a data element. Another way would be a simple count of how many elements have been set to a value (obviously this only works if your data is filled sequentially without any gaps).

answered Aug 11, 2014 at 22:43

TheUndeadFish

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Brian Bi · Accepted Answer · 2014-08-11 22:11:28Z

2

If your question is whether you can distinguish between an element of an array that has been assigned the value zero, versus an element that has not been assigned to but was initialized with the value zero, then the answer is: you cannot.

You will have to find some other way to accomplish what you are trying to accomplish. It's hard to offer specific suggestions because I can't see the broader picture of what you're trying to do.

answered Aug 11, 2014 at 22:11

Brian Bi

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max Over a year ago

I have to read some binary data from a binary file and put them in this array so i can extract specific fields of interesting data from it but it anything goes wrong here it can cause a crash. also 0 is a perfectly valid data.

Vlad from Moscow · Accepted Answer · 2014-08-11 22:16:31Z

0

It depends on whether type quint8 has a bool conversion operator or some other conversion operaror for example to an integer type.

If quint8 is some integral type (some typedef for an integral type) then there is no problem. This definition

quint8 block[16] = { 0 };

initializes all elements of the array by zero.

Take into account that in general case the task can be done with algorithms std::find, std::find_if or std::any_of declared in header <algorithm>

edited Aug 11, 2014 at 22:16

answered Aug 11, 2014 at 22:09

Vlad from Moscow

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