From: Dave Bird <dave AT xemu DOT demon DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Array question (a little bit newbie)
Date: Sat, 6 Mar 1999 18:01:55 +0000
Organization: very little
Message-ID: <DRkChQBT2W42EwAj@xemu.demon.co.uk>
References: <7bllsm$vap$1 AT news5 DOT svr DOT pol DOT co DOT uk> <36E08691 DOT ED519155 AT jps DOT net>
 <7bqquf$2d$1 AT news6 DOT svr DOT pol DOT co DOT uk>
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In article <7bqquf$2d$1 AT news6 DOT svr DOT pol DOT co DOT uk>, Andrew Davidson
<andrew AT lemure DOT freeserve DOT co DOT uk> writes
>>> a little like:
>>>
>>> char *mylist[]= {
>>> "item 1", "item 2", "item 3"
>>> };
>>>
>>> The difference is I don't want a list of pointers to strings, I want
>>> pointers to lists of chars of varying length.
>>
>>Well, you don't say if you are using C or C++.
>>
>>C doesn't know anything about lists of chars of varying length,
>>but, depending on what you mean by that, you CAN do it yourself,
>>with some difficulty.  But you need to be more specific.

  By "list" I presume you simply mean a row of consecutive
  storage spaces, like "FRED" is just {70,82,69,68,0}.
  'C' doesn't know anything about a column of rows which aren't
  all the same length -- doesn't know about  the lengths of
  the individual rows,  or how to compute a combined size by
  adding them up -- so you'd have to handle these things yourself.
  In C++ you would define fancy classes to do it; in 'C' you just
  fiddle and calculate.

  You could define a load of rows of different sizes (they wouldn't
  necessarily be stored together in order), then a column with
  their addresses in.   

  But perhaps you want all the data together?  The best thing would
  be to put it all in a single long row called mydata:

                 /* VEC0          VEC1    VEC2                */
                 /* 00 01 02 03   04 05   06 07 08 09 10 11   */
    char mydata[]={  1, 2, 3, 4,   5, 6,   7, 8, 9, 10,11,12   ....
    };

 The overall length is the length of this:

    int data_length = sizeof(mydata);

 The row pointers would go in an array of pointers:
    
    char (*mylist)[]={ mydata+00, mydata+04,  mydata+06....  };

 And the row-lengths would be stored separately:

    int row_length[]={ 4, 2, 6........};



 Now use it like this:   

    if(j < row_length[i] ){   process(mylist[i][j]);   };

 But don't forget data_length is a different animal from
 sizeof(mylist),  which is the size in bytes of 5 pointers :-< . 
 


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