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Date: Fri, 9 Jan 2015 14:50:16 -0800 (PST)
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Subject: Compiler checking of String lengths during assignment (Newbie
 Question)
From: isaac1.0@gmail.com
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Xref: number.nntp.giganews.com comp.lang.ada:191819
Date: 2015-01-09T14:50:16-08:00
List-Id: <comp.lang.ada>

Maybe this is obvious to the experts, but I'm new to Ada.

I'm using the Libre GNAT GPS 2014. I've a program that looks roughly like t=
his:
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
procedure Main is
   Head : String (1..5) :=3D "XXX_N";
   i : Positive;
   Line : String :=3D "12312312312312312";
  =20
begin
.
.
.
   i :=3D 2;
   Head :=3D "123";
   Head :=3D Line(1 .. 2);
   Head :=3D Line(i+2 .. i+4);
.
.
.
end Main;
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

The first 2 cases produces an error during the build, as expected, because =
Head is known to be length of 5 and I'm assigning something of a different =
length.
The 3rd assignment there does NOT produce an error, no warning no nothing e=
ven though this clearly violates the same check.

What does happen is that at runtime the execution is incorrect. It doesn't =
even terminate in a horrible disaster (which would be preferable). The full=
 program actually just reads a text file (for now) and in this case because=
 the assigned length is incorrect, it just reads a few lines then bails cla=
iming unable to read the text file.

Aren't Ada compilers supposed to prevent stupid errors like this? Or is the=
re some user stupidity here that I'm not seeing...?

Thanks,
Isaac