Pascal Question
Pascal Access Violation when calling a variable in a class
I have made some very simple code in Pascal that is getting me this error:
Project BugFixing.exe raised exception class EAccessViolation with message 'Access violation at address 0040F1EE in module 'BugFixing.exe'. Write of address 00000004'.
The program consists of 2 modules:
BugFixing.dpr:
program BugFixing;
{$APPTYPE CONSOLE}
uses
SysUtils, uLinearProgrammingMainLogic in 'uLinearProgrammingMainLogic.pas', math;
var
MinOrMax : integer ;
Question : TQuestion ;
begin
try
Randomize ;
MinOrMax := RandomRange(0,2) ;
Question.SetMaximiseQuestion(MinOrMax);
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
end.
And uLinearProgrammingMainLogic.pas:
unit uLinearProgrammingMainLogic;
interface
uses sysUtils, math ;
type
TQuestion = class
private
MaximiseQuestion : boolean ;
public
procedure SetMaximiseQuestion (MinOrMax : integer) ;
end;
implementation
procedure TQuestion.SetMaximiseQuestion(MinOrMax : integer);
begin
if MinOrMax = 0 then
MaximiseQuestion := true
else
MaximiseQuestion := false ;
end;
end.
If anyone could explain to me why this is creating an access violation, that'd be appreciated. Thanks in advance. :)
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Answer Source
A class must always be instantiated (TClassType.create) before use. The only exception to that are class/static methods, but you don't declare them that way (and that is not basic usage anyway)
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