On 15 nov 2005, at 17:11, Luis Del Aguila wrote:
Somebody can help me.
I do not understand, that I am making bad.
The program is:
Program ProbandoMemoria;
{$R+}
Var
PLPunteros: ^Pointer;
NuevoTamanio : integer;
elementos : longint;
x,b : ^integer;
Begin
elementos := 3;
NuevoTamanio:=Sizeof(Pointer)*elementos;
ReallocMem(PlPunteros,NuevoTamanio);
Writeln('Direccion : ',longint(Plpunteros) );
new(x);
x^:=7;
Plpunteros^:=x;
b:=Plpunteros^;
Writeln('Direccion : ',longint(b),' valor : ',b^);
new(x);
x^:=15;
(Plpunteros+4)^:=x;
In this statement (and several next ones) you are writing past the
memory allocated for Plpunteros. Adding a value to a pointer,
increases the value of said pointer by this value times the size of
the elements the pointer points to. Since Plpunteros = ^Pointer, the
above writes X to the address "pointer(plpunteros)+4*sizeof(pointer)".
What you want is "(Plpunteros+1)^:=x;". Or, if you are in fpc or
objfpc mode, you can also use "plpunteros[1]:=x;"
b:=(Plpunteros+4)^;
Writeln('Direccion : ',longint(b),' valor : ',b^);
new(x);
x^:=25;
(Plpunteros+8)^:=x;
b:=(Plpunteros+8)^;
Writeln('Direccion : ',longint(b),' valor : ',b^);
//This I do not understand.
//Why ' b^ ' does not have the 7?
Probably because one of the previous out-of-bounds writes overwrote
the value.
Jonas
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