how to create a record

how to create a record

[markww]

Hi,

How can I define a record or a class to this source file and create an
instance of it?

with Ada.Text_IO;

    type struct_device is
        record
           major_number : Integer          := 0;
           minor_number : Integer          := 0;
        end record;

procedure Ada_LinkedList is
begin
   Ada.Text_IO.Put_Line("Hello, world!");
   Ada.Text_IO.Put_Line("just terrible!");
end Ada_LinkedList;


I tried creating a record like in the above example, and compiling with
gnatmake but get the error:

C:\>gnatmake C:\Ada_LinkedList.adb
gcc -c -IC:\ -I- C:\ada_linkedlist.adb
ada_linkedlist.adb:4:05: compilation unit expected
gnatmake: "C:\ada_linkedlist.adb" compilation error

Thanks

Re: how to create a record

[Jeffrey Creem]

markww wrote:
> Hi,
> 
> How can I define a record or a class to this source file and create an
> instance of it?
> 
> with Ada.Text_IO;
> 
>     type struct_device is
>         record
>            major_number : Integer          := 0;
>            minor_number : Integer          := 0;
>         end record;
> 
> procedure Ada_LinkedList is
> begin
>    Ada.Text_IO.Put_Line("Hello, world!");
>    Ada.Text_IO.Put_Line("just terrible!");
> end Ada_LinkedList;
> 
> 
> I tried creating a record like in the above example, and compiling with
> gnatmake but get the error:
> 
> C:\>gnatmake C:\Ada_LinkedList.adb
> gcc -c -IC:\ -I- C:\ada_linkedlist.adb
> ada_linkedlist.adb:4:05: compilation unit expected
> gnatmake: "C:\ada_linkedlist.adb" compilation error
> 
> Thanks
> 

You can't declare anything in Ada in the scope where you declared it. 
Records need to be declared inside of procedures or inside of packages.

So, to do something close to what you appear to be asking for (define 
the record and create an instance of it) try this


  with Ada.Text_IO;
  procedure Ada_LinkedList is
   type struct_device is
          record
             major_number : Integer          := 0;
             minor_number : Integer          := 0;
          end record;

  My_Happy_Record : struct_device;

  begin
     Ada.Text_IO.Put_Line("Hello, world!");
     Ada.Text_IO.Put_Line("just spiffy!");
  end Ada_LinkedList;


A few thoughts though (most of them useless but think about them)

1) You are using two different conventions in your program above. Both 
CamelCase and the Traditional_Ada_Underscore method. Most Ada code tends 
to use _ since that is what the LRM packages do (e.g. text_io) but 
whatever you pick, try to stick with one style

2) Can't really guess where this is going but "struct_device" sounds 
pretty C like. There are no 'structs' in Ada. Again this is just a silly 
style thing and may not matter but it is probably best just live in the 
style of whatever language you use.

3) This is probably the most controvertial statement I'll make. Others 
will disagree...but.. I am not a big fan of the initialize everything in 
the record definition approach. It has its uses. It even makes a lot of 
sense in a lot of cases, but it does not always make sense in every 
case. There are two reasons I dont like it. a - As you start declaring 
local variables of these things in procedures you take the hit of the 
initialization in a lot of cases where you don't need it. yes the 
optimizer can sometimes find those cases....but in practice, they don't. 
b - While this safe practice of initialize everying feels good and 
prevents the read from unitialiazed memory issues, it creates a new kind 
of problem. You can still end up with code where  you expect that some 
path puts some meaningful data into some field but it does not. You feel 
good because it is initialized but in fact, it is still initialized with 
something that is not contextually meaningful. Now, if there is 
something that makes sense, then my all means do it. If not, don't. 
Initializing the fields prevents you from using various cool tools to 
detect problems like this in your code statically (polyspace) or 
dynamically (i.e. gnat with some of its cooler run time checks
(i.e.  http://tinyurl.com/ygrut9)

4) I don't know what it is about Ada but people love the word so much 
they feel the need to say it all the time. Ada_LinkList? Would you have 
written CLinkedList? ...Note this one is a really silly comment and 
probably mostly because it is late. It is always a bad sign when someone 
writes back a response 5x longer than the question when they really have 
only 2 lines worth of useful thoughts.

Re: how to create a record

[jimmaureenrogers]

markww wrote:
> Hi,
>
> How can I define a record or a class to this source file and create an
> instance of it?
>
> with Ada.Text_IO;
>
>     type struct_device is
>         record
>            major_number : Integer          := 0;
>            minor_number : Integer          := 0;
>         end record;
>
> procedure Ada_LinkedList is
> begin
>    Ada.Text_IO.Put_Line("Hello, world!");
>    Ada.Text_IO.Put_Line("just terrible!");
> end Ada_LinkedList;
>

The error message is correct. You are attempting to create a type
outside any compilation unit. You need to either move the record
definition within the procedure, or create a package containing the
record.

If you move the record definition within the procedure it will look
like this:

with Ada.Text_IO;

procedure Ada_Linked_List is
   type Struct_Device is record
      Major_Number : Integer := 0;
      Minor_Number : Integer := 0;
   end record;
begin
   Ada.Text_IO.Put_Line("Hello World!");
   Ada.Text_IO.Put_Line("just terrible!");
end Ada_Linked_List;

Jim Rogers

Re: how to create a record

[Jeffrey R. Carter]

markww wrote:
> 
> with Ada.Text_IO;
> 
>     type struct_device is
>         record
>            major_number : Integer          := 0;
>            minor_number : Integer          := 0;
>         end record;

This is a declaration. It goes in a declarative region, between "is" and 
"begin".

> procedure Ada_LinkedList is

Like here.

> begin
>    Ada.Text_IO.Put_Line("Hello, world!");
>    Ada.Text_IO.Put_Line("just terrible!");
> end Ada_LinkedList;
> 
> I tried creating a record like in the above example, and compiling with
> gnatmake but get the error:

What you have is a record type declaration. To create a record object 
you have to declare an object of the type:

Object : Struct_Device;

Since you declare no objects of the type, the declaration serves no 
purpose, so you can achieve the same effect by deleting the type 
declaration.

-- 
Jeff Carter
"I soiled my armor, I was so scared."
Monty Python & the Holy Grail
71

Re: how to create a record

[Jeffrey R. Carter]

Jeffrey Creem wrote:
> 
> 1) You are using two different conventions in your program above. Both 
> CamelCase and the Traditional_Ada_Underscore method. Most Ada code tends 
> to use _ since that is what the LRM packages do (e.g. text_io) but 
> whatever you pick, try to stick with one style

If you do use CamelCase, many of us will run your code through 
reformatters that will change it to Camelcase. If you don't like seeing 
that, use underscores to separate words in identifiers.

> 2) Can't really guess where this is going but "struct_device" sounds 
> pretty C like. There are no 'structs' in Ada. Again this is just a silly 
> style thing and may not matter but it is probably best just live in the 
> style of whatever language you use.

There are also no switch statements, no breaks, no casts, ...

Using such terms implies (usually correctly) thinking at the low-level 
of most C code. Ada code is often much higher level. Using the Ada terms 
helps indicate that you're thinking at that higher lever (or helps 
pretend that you are; all this stuff about the Language Shootout is 
really concerned with low-level stuff that is an elephant most of the time).

Also, this is an Ada newsgroup; understanding C terms is not a 
requirement. You can be sure your audience understands you by using Ada 
terms here.

-- 
Jeff Carter
"I soiled my armor, I was so scared."
Monty Python & the Holy Grail
71

Re: how to create a record

[Maciej Sobczak]

Jeffrey Creem wrote:

> 4) I don't know what it is about Ada but people love the word so much 
> they feel the need to say it all the time. Ada_LinkList? Would you have 
> written CLinkedList?

Actually, there are C++ programmers that put 'C' in front of *every* 
class name. And it's not to compensate for the lack of namespaces in 
some stone-age compilers, it's just to say "this is a class".

I guess that it's Microsoft's MFC framework/library that promoted it 
most widely with its broken variant of what was initially a "Hungarian 
Notation". For your amusement:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vclib/html/_mfc_hierarchy_chart.asp


-- 
Maciej Sobczak : http://www.msobczak.com/
Programming    : http://www.msobczak.com/prog/

Re: how to create a record

[Martin Krischik]

markww schrieb:

> C:\>gnatmake C:\Ada_LinkedList.adb
> gcc -c -IC:\ -I- C:\ada_linkedlist.adb
> ada_linkedlist.adb:4:05: compilation unit expected
> gnatmake: "C:\ada_linkedlist.adb" compilation error

Your question has been answered, so just some suggested reading:

http://en.wikibooks.org/wiki/Ada_Programming/Packages

Martin

Re: how to create a record

[Pascal Obry]

markww a �crit :
> How can I define a record or a class to this source file and create an
> instance of it?

Frankly, the first thing to do would be to read an Ada text book. The
code you post is not Ada! You are going to loose lot of time learning
using comp.lang.ada!

Pascal.

-- 

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--|------------------------------------------------------
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Re: how to create a record

[Randy Brukardt]

"Pascal Obry" <pascal@obry.net> wrote in message
news:454B74BB.6020900@obry.net...
...
> Frankly, the first thing to do would be to read an Ada text book. The
> code you post is not Ada! You are going to loose lot of time learning
> using comp.lang.ada!

Of which there are many on-line: see
http://www.adaic.com/learn/textbook.html for a listing of textbooks, and
http://www.adaic.com/free/freebook.html for a listing of those available
online. And look at the entire "learning Ada" section
(http://www.adaic.com/learn/index.html) for more resources.

               Randy Brukardt (AdaIC Technical Webmaster)