Difference between revisions of "Dynamic array"

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The dynamic array type is very similar to the [[array|array]] type, but it allows more flexibility since the number of elements does not need to be known until the program execution.
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The dynamic array type is very nice feature of the freepascal compiler. It is very similar to the [[array|array]] type, but it allows more flexibility since the number of elements does not need to be known until the program execution.
  
 
The declaration part is just as simple as the [[array|array]] type:   
 
The declaration part is just as simple as the [[array|array]] type:   
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   ...
 
   ...
 
   <b>end</b>
 
   <b>end</b>
You can put as many <b>SetLength</b> statements as you want in your program in order to expand, or truncate an array but you must put at least one before you can use the variable for the first time.  
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You can put as many <b>SetLength</b> statements as you want in your program in order to expand, or truncate an array but you must put at least one statement before you can use the variable for the first time.  
  
 
The individual elements can be accessed as usual:
 
The individual elements can be accessed as usual:
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   MyVariable[18] := 123;
 
   MyVariable[18] := 123;
 
   ...
 
   ...
   MyOtherVariable := Myvariable[0];
+
   MyOtherVariable := MyVariable[0];
 
   ...
 
   ...
  
 
The index of a dynamic array is ZERO based, ie. it must be whittin the range from 0 to (Length-1). It is not possible to change this to a ONE based system.
 
The index of a dynamic array is ZERO based, ie. it must be whittin the range from 0 to (Length-1). It is not possible to change this to a ONE based system.
  
 +
As the program or the procedure exits, the variable is removed and the computer memory is available again. This behaviour suggest that the stack memory is used but the freepascal dynamic memory management system is inserted in the executable program and is totally transparent to the programmer. 
 
[[category:Pascal]]
 
[[category:Pascal]]

Revision as of 02:45, 16 January 2010

The dynamic array type is very nice feature of the freepascal compiler. It is very similar to the array type, but it allows more flexibility since the number of elements does not need to be known until the program execution.

The declaration part is just as simple as the array type:

 var
 ...
 MyVariable : array of type;
 ...

The number of elements can be set or modified whenever needed during the execution of the program by using the statement:

 begin
 ...
  SetLength (MyVariable, ItsNewLength);
 ...
 end

You can put as many SetLength statements as you want in your program in order to expand, or truncate an array but you must put at least one statement before you can use the variable for the first time.

The individual elements can be accessed as usual:

 ...
 MyVariable[18] := 123;
 ...
 MyOtherVariable := MyVariable[0];
 ...

The index of a dynamic array is ZERO based, ie. it must be whittin the range from 0 to (Length-1). It is not possible to change this to a ONE based system.

As the program or the procedure exits, the variable is removed and the computer memory is available again. This behaviour suggest that the stack memory is used but the freepascal dynamic memory management system is inserted in the executable program and is totally transparent to the programmer.