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digitalmars.D.learn - Bidimensional dynamic array problem

reply orgoton <orgoton mindless.com> writes:
I have this

struct Vertex{
(...)
float z;
}

then:
Vertex vData[][];

Somewhere later:
vData.length=sizeX;
foreach(Vertex strip[]; vData[]) strip.length=sizeY;

Here the array is initialized. So far, I think I haven't done anything illegal.
(SizeX and SizeY are runtime values, ushort vars). So first I say how many
strips I want, and next, I put in how many elements that strip will have.

ulong m;
foreach (Vertex[] strip; vData)
{
      foreach (Vertex vertex; strip)
      {
           file.read(vertex.height);
           m++;
      }
}

Here I read the values from a file. First, I select a strip, and then go
through all the elements of that array and read their values. "m" is a counter
to see how many elements where read.

The thing is, m=0 at the end of the loop. What did I do wrong?
Mar 06 2007
next sibling parent orgoton <orgoton mindless.com> writes:
Just a minor correction:

 struct Vertex{
 (...)
 float z;
 }


should be

struct Vertex{
(...)
float height;
}

(typo)
Mar 06 2007
prev sibling next sibling parent reply Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:
orgoton wrote:

 I have this
 
 struct Vertex{
 (...)
 float z;
 }
 
 then:
 Vertex vData[][];
 
 Somewhere later:
 vData.length=sizeX;
 foreach(Vertex strip[]; vData[]) strip.length=sizeY;


foreach(inout Vertex[] strip; vData) strip.length = sizeY;
or just:
foreach(inout strip; vData) strip.length = sizeY;

Note: only the inout is significant, the rest is just nitpicking :P.
If you don't specify 'inout', you're just modifying a local copy of the 
element...

And IIRC something like "vData = new Vertex[][](sizeX, sizeY)" should 
replace that entire code sequence, initializing the outer array to an 
array of sizeX arrays of length sizeY.


 Here the array is initialized. So far, I think I haven't done anything
illegal. (SizeX and SizeY are runtime values, ushort vars). So first I say how
many strips I want, and next, I put in how many elements that strip will have.


You haven't done anything illegal, just something wrong ;).
You haven't initialized the array the way you thought you did: it's just 
an array of _empty_ dynamic arrays at this point.


 ulong m;
 foreach (Vertex[] strip; vData)


(this loop doesn't require 'inout' since the array itself isn't 
modified, just the data it references)


 {
       foreach (Vertex vertex; strip)


foreach(inout Vertex vertex; strip)
(or: foreach(inout vertex; strip))


       {
            file.read(vertex.height);
            m++;
       }
 }
 
 Here I read the values from a file. First, I select a strip, and then go
through all the elements of that array and read their values. "m" is a counter
to see how many elements where read.
 
 The thing is, m=0 at the end of the loop. What did I do wrong?


Since you didn't initialize the elements of vData, their lengths are all 
still zero. So your inner loop is never executed.
Mar 06 2007
parent Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:
Frits van Bommel wrote:

 orgoton wrote:
 

 ulong m;
 foreach (Vertex[] strip; vData)


 
 (this loop doesn't require 'inout' since the array itself isn't 
 modified, just the data it references)


Sorry, that's not right. Not even the data is modified, just the data 
referenced *by* the data...


 {
       foreach (Vertex vertex; strip)


 
 foreach(inout Vertex vertex; strip)
 (or: foreach(inout vertex; strip))
 

       {
            file.read(vertex.height);
            m++;
       }
 }
Mar 06 2007
prev sibling parent orgoton <orgoton mindless.com> writes:
Frits van Bommel Wrote:


 orgoton wrote:

 I have this
 
 struct Vertex{
 (...)
 float z;
 }
 
 then:
 Vertex vData[][];
 
 Somewhere later:
 vData.length=sizeX;
 foreach(Vertex strip[]; vData[]) strip.length=sizeY;


 
 foreach(inout Vertex[] strip; vData) strip.length = sizeY;
 or just:
 foreach(inout strip; vData) strip.length = sizeY;
 
 Note: only the inout is significant, the rest is just nitpicking :P.
 If you don't specify 'inout', you're just modifying a local copy of the 
 element...
 
 And IIRC something like "vData = new Vertex[][](sizeX, sizeY)" should 
 replace that entire code sequence, initializing the outer array to an 
 array of sizeX arrays of length sizeY.
 

 Here the array is initialized. So far, I think I haven't done anything
illegal. (SizeX and SizeY are runtime values, ushort vars). So first I say how
many strips I want, and next, I put in how many elements that strip will have.


 
 You haven't done anything illegal, just something wrong ;).
 You haven't initialized the array the way you thought you did: it's just 
 an array of _empty_ dynamic arrays at this point.
 

 ulong m;
 foreach (Vertex[] strip; vData)


 
 (this loop doesn't require 'inout' since the array itself isn't 
 modified, just the data it references)
 

 {
       foreach (Vertex vertex; strip)


 
 foreach(inout Vertex vertex; strip)
 (or: foreach(inout vertex; strip))
 

       {
            file.read(vertex.height);
            m++;
       }
 }
 
 Here I read the values from a file. First, I select a strip, and then go
through all the elements of that array and read their values. "m" is a counter
to see how many elements where read.
 
 The thing is, m=0 at the end of the loop. What did I do wrong?


 
 Since you didn't initialize the elements of vData, their lengths are all 
 still zero. So your inner loop is never executed.



That did it! Thanks a lot. I feel illuminated :P
Mar 06 2007