String types and relational operators - Gpc

1 May 2000


      We are using for teaching purposes the GPC compiler under Linux
(RedHat 6.1) which was installed from the following RPM packages:
gpc-19990118-1.i386.rpm 
    gpc-extras-19990118-1.i386.rpm
Our Pascal programs are compiled with the "--borland-pascal" option.
I noticed a problem with the type "String" (and the derived types like
"String[10]") and the relational operators which do not seem to return
correct results.  The following test program seems illustrate this
point:
----------------------------------------------------------------------
program test;
procedure Compare(var x,y :  String);
begin
   if x=y
     then Writeln('"',x,'" = "',y,'"')
     else 
   if x>y
     then Writeln('"',x,'" > "',y,'"')
     else 
   if x<y
     then Writeln('"',x,'" < "',y,'"')
     else Writeln('"',x,'" ? "',y,'"')
end; { Compare }
var a,b	       : String;
   Empty,Zeros : String;
begin
   a := 'abcd';
   b := 'abce';
   Empty := '';
   Zeros := '0000';
   Compare(Zeros,Zeros);
   Compare(Zeros,a);
   Compare(a,Zeros);
   Compare(Empty,Empty);
   Compare(Empty,a);
   Compare(a,Empty);
   Compare(a,a);
   Compare(a,b)
end.
----------------------------------------------------------------------
The following output was produced:
"0000" = "0000"
"0000" > "abcd"      [*]
"abcd" ? "0000"      [*]
"" = ""
"" > "abcd"          [*]
"abcd" ? ""          [*]
"abcd" = "abcd"
"abcd" > "abce"      [*]
which shows that some results are wrong (marked with [*]).
Any suggestions as to what might be wrong?
-- Tomasz Kowaltowski