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POAda CONSTRAINT_ERROR not being raised when it "should"
 

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    <p>I've been looking through this <a href="http://www.infres.enst.fr/~pautet/Ada95/e_c03_p4.ada" rel="nofollow">Ada 95 tutorial</a>. I was reading that it is possible to define a type that has a range that is different than the standard range, and if the program tries to go outside this range it will throw an error. While working on my own program I noticed that if the end of the range in the definition falls on the boundary for of its underlying type then the program will not raise the CONSTRAINT_ERROR when assigning values out of that range. Instead it will happily keep going and then wrap around. I wrote a program to explicitly show this.</p> <p>Does anyone know of an Ada rule that explains this behavior?</p> <p>-Kirk</p> <p>Here is the output from my terminal, the source code is below that.</p> <pre><code>me@acheron:~/Dropbox/programs/ada$ gnatmake constraints.adb -f gcc-4.6 -c constraints.adb gnatbind -x constraints.ali gnatlink constraints.ali me@acheron:~/Dropbox/programs/ada$ ./constraints Type ON has size: 7 It has a min/max of: 0 127 It's base has a min/max of: -128 127 Type UNDER has size: 7 It has a min/max of: 0 126 It's base has a min/max of: -128 127 The value of No_Error is: 245 raised CONSTRAINT_ERROR : constraints.adb:58 range check failed me@acheron:~/Dropbox/programs/ada$ </code></pre> <p>Source Code:</p> <pre><code>with Ada.Text_IO, Ada.Integer_Text_IO; use Ada.Text_IO, Ada.Integer_Text_IO; Procedure Constraints is type UNDER is range 0..126; type ON is range 0..127; type OVER is range 0..128; Error : UNDER := 0; No_Error : ON := 0; Index : INTEGER := 0; begin New_Line; Put("Type ON has size: "); Put(INTEGER(ON'SIZE)); New_Line; Put("It has a min/max of: "); Put(INTEGER(ON'FIRST)); Put(INTEGER(ON'LAST)); New_Line; Put("It's base has a min/max of: "); Put(INTEGER(ON'BASE'FIRST)); Put(INTEGER(ON'BASE'LAST)); New_Line; New_Line; Put("Type UNDER has size: "); Put(INTEGER(UNDER'SIZE)); New_Line; Put("It has a min/max of: "); Put(INTEGER(UNDER'FIRST)); Put(INTEGER(UNDER'LAST)); New_Line; Put("It's base has a min/max of: "); Put(INTEGER(UNDER'BASE'FIRST)); Put(INTEGER(UNDER'BASE'LAST)); Safe_Loop: loop No_Error := No_Error + 1; Index := Index + 1; --Put(INTEGER(No_Error)); exit Safe_Loop when Index = 245; end loop Safe_Loop; New_Line; Put("The value of No_Error is: "); Put(INTEGER(No_Error)); Index := 0; Crash_Loop: loop Error := Error + 1; Index := Index + 1; exit Crash_Loop when Index = 245; end loop Crash_Loop; end Constraints; </code></pre>
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