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digitalmars.D.learn - noob Q: array out-of-range

reply Duke Normandin <dukeofperl ml1.net> writes:
Hey...

Compiler is now working as expected! Thank's to a great catch by
Michel Fortin!

A little further down the tutorial "D_ A Newbie-Oriented Tutorial",
there's this code:

[code]
import std.stdio;

void main()
{
	int[] intArray;

  intArray[0] = 42;
  intArray[1] = 54;
  intArray[2] = 91;

  writefln("The lemgth of the intArray is %d.",
         intArray.length);
}
[/code]

It compiles with no error or warning - AFAICT. However, it chokes
upon execution with:

dnormandin  ~/programming/dmd2/code
01:40 pm >> arrays_in_d
core.exception.RangeError arrays_in_d(7): Range violation

I've read and re-read the tutorial content, but it's not jumping out
at me.
-- 
duke
May 28 2010
parent reply Don <nospam nospam.com> writes:
Duke Normandin wrote:

 Hey...
 
 Compiler is now working as expected! Thank's to a great catch by
 Michel Fortin!
 
 A little further down the tutorial "D_ A Newbie-Oriented Tutorial",
 there's this code:
 
 [code]
 import std.stdio;
 
 void main()
 {
 	int[] intArray;
 
   intArray[0] = 42;
   intArray[1] = 54;
   intArray[2] = 91;
 
   writefln("The lemgth of the intArray is %d.",
          intArray.length);
 }
 [/code]
 
 It compiles with no error or warning - AFAICT. However, it chokes
 upon execution with:
 
 dnormandin  ~/programming/dmd2/code
 01:40 pm >> arrays_in_d
 core.exception.RangeError arrays_in_d(7): Range violation
 
 I've read and re-read the tutorial content, but it's not jumping out
 at me.


The array initially has length of zero.
You need to write something like:
intArray = new int[3];
or
intArray.length = 3;
before putting anything into it.
May 28 2010
parent reply bearophile <bearophileHUGS lycos.com> writes:
Don:

 The array initially has length of zero.
 You need to write something like:
 intArray = new int[3];
 or
 intArray.length = 3;
 before putting anything into it.


In some languages (Perl? Maybe Lua and PHP) arrays auto-create empty slots as
needed, but in many languages you need to tell the language that you want some
empty slots before you can put values inside them (this stricter behaviour can
probably catch some bugs, and allows to produce faster programs).

Another way to add items to a D dynamic array like intArray is to append them
at the end, the language runtime takes care of creating new slots as needed:

int[] intArray;
intArray ~= 1;
intArray ~= 2;
intArray ~= 3;

Bye,
bearophile
May 28 2010
parent reply Duke Normandin <dukeofperl ml1.net> writes:
On Fri, 28 May 2010, bearophile wrote:


 Don:

 The array initially has length of zero.
 You need to write something like:
 intArray = new int[3];
 or
 intArray.length = 3;
 before putting anything into it.


 In some languages (Perl? Maybe Lua and PHP) arrays auto-create empty slots as
needed, but in many languages you need to tell the language that you want some
empty slots before you can put values inside them (this stricter behaviour can
probably catch some bugs, and allows to produce faster programs).

 Another way to add items to a D dynamic array like intArray is to append them
at the end, the language runtime takes care of creating new slots as needed:

 int[] intArray;
 intArray ~= 1;
 intArray ~= 2;
 intArray ~= 3;

 Bye,
 bearophile



 Don
 bearophile

Would you guys visit this URL real quick

http://compsci.ca/v3/viewtopic.php?t=9518

This is the site that I'm using to learn D. If you scroll down 3-4
screens full, you'll come to the "array" topic. Is this tutorial
outdated, wrong, or what, because it doesn't deem to sync with what
you two fine fellows are telling me about creating dynamic arrays in
the D-Language. TIA..
-- 
duke
May 28 2010
parent reply bearophile <bearophileHUGS lycos.com> writes:
Duke Normandin:


 This is the site that I'm using to learn D. If you scroll down 3-4
 screens full, you'll come to the "array" topic. Is this tutorial
 outdated, wrong, or what, because it doesn't deem to sync with what
 you two fine fellows are telling me about creating dynamic arrays in
 the D-Language. TIA..


That part of that tutorial is not outdated, as far as I know it's just wrong.
You can auto-create slots in associative arrays:

int[int] aa;
aa[0] = 1;
aa[1] = 1;
aa[2] = 1;

Lua language uses associative arrays instead of arrays :-)

Bye,
bearophile
May 28 2010
parent reply Duke Normandin <dukeofperl ml1.net> writes:
On Fri, 28 May 2010, bearophile wrote:


 Duke Normandin:


 This is the site that I'm using to learn D. If you scroll down 3-4
 screens full, you'll come to the "array" topic. Is this tutorial
 outdated, wrong, or what, because it doesn't deem to sync with what
 you two fine fellows are telling me about creating dynamic arrays in
 the D-Language. TIA..


 That part of that tutorial is not outdated, as far as I know it's just wrong.
 You can auto-create slots in associative arrays:

 int[int] aa;
 aa[0] = 1;
 aa[1] = 1;
 aa[2] = 1;

 Lua language uses associative arrays instead of arrays :-)

 Bye,
 bearophile



So these two paragraphs in the tutorial are flat out wrong?

[quote]
You should note that I never specified how long the array should be.
Instead I simply assigned values to various positions in the array and
it just worked.
This is an example of a dynamic array. It will grow to whatever size
is required. I can determine the size of an array at any time by
accessing the array's length property. The length property can also
have a value assigned to it to resize the array.
[/quote]

Maybe the link for this tutorial at:

http://www.prowiki.org/wiki4d/wiki.cgi?FirstLanguage

should be removed?

-- 
duke
May 28 2010
parent reply "Simen kjaeraas" <simen.kjaras gmail.com> writes:
Duke Normandin <dukeofperl ml1.net> wrote:


 So these two paragraphs in the tutorial are flat out wrong?


Absolutely.

-- 
Simen
May 28 2010
next sibling parent reply Duke Normandin <dukeofperl ml1.net> writes:
On Sat, 29 May 2010, Simen kjaeraas wrote:


 Duke Normandin <dukeofperl ml1.net> wrote:


 So these two paragraphs in the tutorial are flat out wrong?


 Absolutely.


Then I'm done with _that_ site - can't trust it!

Any chance that you could suggest a good beginner's D tutorial?

-- 
duke
May 28 2010
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Fri, 28 May 2010 22:42:32 -0400, Duke Normandin <dukeofperl ml1.net>  
wrote:


 On Sat, 29 May 2010, Simen kjaeraas wrote:


 Duke Normandin <dukeofperl ml1.net> wrote:


 So these two paragraphs in the tutorial are flat out wrong?


 Absolutely.


 Then I'm done with _that_ site - can't trust it!

 Any chance that you could suggest a good beginner's D tutorial?


It's quite possible that the example code *worked* at some very early  
version of the D compiler.

Nowadays, all arrays are initialized with null as the pointer,  
guaranteeing that the first time you access array[0], it will segfault.   
So with the current compilers, that code is *guaranteed* to not work.

I speak not from experience, ever since I've started using D it always  
initializes arrays to null.  I just can't imagine that someone would have  
written such a tutorial without having some experience with D, and without  
ever having compiled the code.  So my logical conclusion is that either 1)  
at some point, that code did work, 2) the author was so convinced of his D  
mastery that he didn't bother to try any of his examples, or 3) the page  
is a blatant attempt to make users not like D.

I find 2 unlikely since he specifically mentions how you don't have to  
initialize arrays.

I wonder if someone recalls the feature set of the dmd compiler from July,  
2005.

-Steve
May 28 2010
parent "Simen kjaeraas" <simen.kjaras gmail.com> writes:
Steven Schveighoffer <schveiguy yahoo.com> wrote:


 I wonder if someone recalls the feature set of the dmd compiler from  
 July, 2005.


That would be http://ftp.digitalmars.com/dmd.128.zip

Tested the example given with that compiler, and got ArrayBoundsError.
Just as expected.

-- 
Simen
May 29 2010
prev sibling parent BCS <none anon.com> writes:
Hello Simen,


 Duke Normandin <dukeofperl ml1.net> wrote:
 

 So these two paragraphs in the tutorial are flat out wrong?
 


 Absolutely.
 


Any idea who owns it so it can get changed? For that matter, who added the 
link?

Being paranoid for the moment (it can be fun sometimes :) that blurb is so 
wrong that I wonder if it's an attempt to frustrate newbies away from D?

-- 
... <IXOYE><
May 28 2010