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Cross Ref > Data Structures

By Mike Prestwood

PHP versus Corel Paradox: A side by side comparison between PHP and Corel Paradox.

 
Data Structures
 

Data structures allow you to store and work with data. Common data structures include arrays, associative arrays, etc.

Array

[Other Languages] 

Languages Focus

A data structure in which individual values (called elements or items) may be located by reference to one or more integer index variables, the number of such indices being the number of dimensions in the array.

Arrays can start with an index value of 0 or 1, sometimes referred to as 0 based or 1 based.

[Not specified yet. Coming...]
Corel Paradox:   Array[] type

Arrays in ObjectPAL use a 1-based subscript (also known as an index). Use [] with a subscript to refer to an element (i.e. MyArray[1], MyArray[2]).

The number of elements for a given array in ObjectPAL are either fixed or resizeable. Specify the size when you declare it for fixed. Use size() to get the number of elements, size() returns 0 if the array has no elements. Use setSize(), grow(), addLast(), etc. to add elements to an array.

Syntax Example:

var
  MyArray Array[4] String ;Fixed size array.
  i LongInt
endVar

MyArray[1] = "Mike"
MyArray[2] = "Lisa"
MyArray[3] = "Felicia"
MyArray[4] = "Nathan"

if MyArray.size() > 0 then
  for i from 1 to MyArray.size()
    msgInfo("", MyArray[i])
  endFor
endIf





Associative Array

[Other Languages] 
A set of unique keys linked to a set of values. Each unique key is associated with a value. Think of it as a two column table. MyArray['CA'] = 'California' MyArray['AR'] = 'Arizona'

Languages Focus

Associative arrays are also known as a dictionary or a hash table in other languages.

PHP: 

Declare associative array with initial known values. You can also add to associative array. (You can just assign values without ever declaring it too!)

Syntax Example:
$prices = array( 'Tires'=>100, 'Spark Plugs'=>4 );
$prices['Oil'] = 10;
 
echo "Tires=" . $prices['Tires'] . "<br>";
echo "Oil=" . $prices['Oil'] . "<br>";
Corel Paradox:   DynArray

In ObjectPAL associative arrays are known as dynamic arrays.

Syntax Example:
var
myDynArray   DynArray[] String
endVar

 
myDynArray["Last_Name"] = "Spitz"
myDynArray["First_Name"] = "Randy"
myDynArray.view()




Pointers

[Other Languages] 

General Info: Pointers / References

A pointer is a variable type that allows you to refer indirectly to another object. Instead of holding data, a pointer holds the address to data -- the address of another variable or object. You can change the address value a pointer points to thus changing the variable or object the pointer is pointing to.

A reference is a type of pointer that cannot change and it must always point to a valid storage (no nulls).

PHP:   Not Supported

PHP supports references which allow you to refer to the value of a variable but PHP does not support true developer defined pointers. You cannot get and use the address of a variable.

However, you can still do inexpensive assignments by assigning by reference.

Corel Paradox: 

ObjectPAL doesn't have a developer defined pointer type except for use with DLLs where you use a special CPTR uses keyword to refer to a DLL string pointer data type.

Syntax Example:  
Uses Tapi32
  tapiRequestMakeCall(sNumber CPTR, sAppName CPTR, 
    sLogName CPTR, sComment CPTR) CLONG
endUses




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