These are two linked lists that I've made,for a school project... I want the first list to be called from the second,I have done that and at the compile time everything is ok. When I run it it says : Project (myProject) raised exception class 'External: SIGSEGV'. At address 40D32D Here is my code:
list2=^ptr;
ptr=record
vlera:integer;
pozicioni:integer;
end;
type
list=^pointer;
pointer=record
rreshti:list2;
end;
var
a:array[1..7] of list;
i:integer;
kjovlere:list2;
begin
for i:=1 to 7 do begin
a[i]:=@kjovlere;
write('Give the pozition for the row:',i,' : ');
read(a[i]^.rreshti^.pozicioni);
write ('give the value for this poziton :');
read(a[i]^.rreshti^.vlera);
writeln;
end;
end.
And the error is at the for loop,at the read(a[i]^.rreshti^.pozicioni);
I would be very thankful if anyone explains me or gives me any suggestion :)
The provided source code shows at least two misunderstandings about pointer management in Pascal.
Main Problem - To assign data, a
recordtype shall be allocated before.
This problem is referring to the lines read(a[i]^.rreshti^.pozicioni); and read(a[i]^.rreshti^.vlera);.
Both a[i] and rreshti are declared as pointer type (list=^pointer; & list2=^ptr;) and shall be allocated to a record structure before assigning data.
Step1: allocate the a[i] pointer in the loop.
new(a[i]);
Step2: allocate the a[i]^.rreshti pointer in the loop.
new(a[i]^.rreshti);
Strange Problem - Assign a pointer to a
recordtype shall respect the destination type.
This problem is referring to the line a[i]:=@kjovlere;.
The a[i] is a list which is list=^pointer; and not list2 (list2=^ptr;) as declared for kjovlere:list2;.
Solution is: remove that line a[i]:=@kjovlere;.
Solution:
begin
for i:=1 to 7 do begin
(* a[i]:=@kjovlere; to be removed *)
new(a[i]);
new(a[i]^.rreshti);
write('Give the pozition for the row:',i,' : ');
read(a[i]^.rreshti^.pozicioni);
write ('give the value for this poziton :');
read(a[i]^.rreshti^.vlera);
writeln;
end;
end.