Alvin Oga <[EMAIL PROTECTED]> wrote on 24/01/2002 (11:13) :
>
> hi ya ralf
>
> i would have thought that gcc would barf on b[20]='X'
> and similarly for theother variable assignments since its not prev
> allocated/defined.. and yet explicitly assigned (incorrectly??)...
Why there are no range tests in C.
Lets do it Ada 95 instead:
I have tired to make the code as similar to C as possible so it is a bit
ackward Ada-wise but here goes:
Note I have written here the line numbers in front of the code so that
it is easier to check with the compiler results.
file: example.adb
------------------------------------------------------------------------
1 with Ada.Text_IO; use Ada.Text_IO; -- equvalent to #include <stdio.h>
2
3 procedure example is
4 -- Ada has it's own String type, but lets do what the C example does.
5 type C_String_Type is array (1..10) of Character;
6
7 a : C_String_type;
8 b : C_String_type;
9 begin
10
11 a := ('1','2','3','4','5','6','7','8','9', others => ' ');
12 -- others => ' ' just means that the rest of the array will be
13 -- filled with spaces.
14
15 -- Printing a becomes ackward as I didn't use the Ada Strings type
16 -- in this example, but as you can see the for loop is nice.
17
18 Put ("a: ");
19 for i in C_String_Type'Range loop
20 Put (a(i));
21 end loop;
22
23 New_Line;
24
25 -- Now the faulty code.
26 b (20) := 'X';
27 b (21) := 'Y';
28 b (22) := 'Z';
29
30 -- No point in printing again as the code will never reach here.
31 end example;
------------------------------------------------------------------------
Now when compiling we get:
% gnatmake example.adb
gnatgcc -c example.adb
example.adb:26:07: warning: value not in range of subtype of
"Standard.integer" defined at line 5
example.adb:26:07: warning: "constraint_error" will be raised at run time
example.adb:27:07: warning: value not in range of subtype of
"Standard.integer" defined at line 5
example.adb:27:07: warning: "constraint_error" will be raised at run time
example.adb:28:07: warning: value not in range of subtype of
"Standard.integer" defined at line 5
example.adb:28:07: warning: "constraint_error" will be raised at run time
gnatbind -x example.ali
gnatlink example.ali
And if one ignore the wranings and run the program:
% ./example
a: 123456789
raised CONSTRAINT_ERROR : example.adb:26
So as the compiler said the code would not run without a constraint
error being raised at line 26 which is the faulty code.
Preben Randhol
--
«For me, Ada95 puts back the joy in programming.»
