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Newsgroups: comp.lang.ada
Date: Wed, 22 Oct 2014 10:44:27 -0700 (PDT)
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Subject: Re: Assembling Complex Strings Containing Carriage Returns Prior to
 Using Ada.Text_IO.Put?
From: Adam Beneschan <adambeneschan@gmail.com>
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Xref: number.nntp.giganews.com comp.lang.ada:189978
Date: 2014-10-22T10:44:27-07:00
List-Id: <comp.lang.ada>

On Tuesday, October 21, 2014 10:57:39 PM UTC-7, NiGHTS wrote:
> I am converting some code from C to Ada which involves building a complex=
 string containing '\n' characters which would eventually be displayed on t=
he standard output console using the printf() function.=20

> I tried to copy the same strategy of building the string in Ada like this=
:

> Complex_String : Ada.Strings.Unbounded.Unbounded_String;
>=20
> EOL            : String :=3D ASCII.CR'Img;

As others have pointed out, 'Img is a GNAT-defined attribute; it depends on=
 the Ada-defined attribute 'Image.  'Image is not intended to convert a Cha=
racter to a one-character String.  If you say

    C : Character :=3D 'x';
    S : String :=3D Character'Image (C);

S will have length 3 and will be "'x'".

Character is an enumeration type in Ada, although it's somewhat special.  B=
ut the rules for 'Image (and its converse, 'Value) are the same as for othe=
r enumeration types: they give you (or expect) a string that looks like wha=
t the enumeration value would look like in the enumeration declaration.  Fo=
r example, with this enumeration type:

    type Color is (RED, GREEN, BLUE);

the 'Image attribute will produce "RED", "GREEN", or "BLUE".  (It's always =
upper-case for identifiers.)  And for an enumeration type that has characte=
r literals mixed in:

    type Whatsit is (This, That, '?');

'Image will produce "THIS", "THAT", or "'?'".  (What makes Character specia=
l is that if you give it a non-printable character, there are special rules=
 for what 'Image returns; in your case it returned "CR".)

                            -- Adam