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Free Pascal => FPC development => Topic started by: nouzi on April 14, 2019, 10:15:04 am

Title: About the FPC feature
Post by: nouzi on April 14, 2019, 10:15:04 am

About the FPC feature
You could see this expression

Code: Pascal  [Select][+][-]

1. try
2.  
3.    try
4.  
5.    finally
6.  
7.    end;
8.  
9. Except
10. end;
11.  

In one expression

Code: Pascal  [Select][+][-]

1. try
2.   finally
3.   Except
4. end;
5.  

or

Code: Pascal  [Select][+][-]

1. [code=pascal]
2. try
3.  Except
4.  finally
5. end;
6.  

[/code]
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Title: Re: About the FPC feature
Post by: Thaddy on April 14, 2019, 10:24:02 am

Quote from: nouzi on April 14, 2019, 10:15:04 am

About the FPC feature

Try finally end; is used to make sure a reference counted or dynamically allocated resource is always released, e.g:

Code: Pascal  [Select][+][-]

1. var a:Tobject;
2. begin
3.   a:=Tobject.create;
4.   try
5.      // do something with a.
6.   finally
7.     a.free; Now after use clean up the instance
8.   end;

Try except end; is to catch any exceptions that can be caused in the try block and handle those gracefully, e.g.

Code: Pascal  [Select][+][-]

1. var a,b:integer;
2. begin
3.    try
4.       a:=1;
5.       b:=0;
6.       a :=a div b;
7.    except
8.        writeln('division by zero');
9.    end;

Your last example is nonsense and should be:

Code: Pascal  [Select][+][-]

1. try
2.   try
3.   except
4.   end;
5. finally
6. end;

   

Title: Re: About the FPC feature
Post by: nouzi on April 14, 2019, 10:47:22 am

What if I merging the first and second expressions? According to my understanding we get

Code: Pascal  [Select][+][-]

1. var
2.  a,b:integer;
3.  c:Tobject;
4.   begin
5.     c:=Tobject.create;
6.  
7.     try
8.        // do something with a.
9.     finally
10.       c.free; //Now after use clean up the instance
11.     end;
12.  
13.       try
14.  
15.         a:=1;
16.         b:=0;
17.         a :=a div b;
18.      except
19.          writeln('division by zero');
20.      end;  
21.  

or this code

Code: Pascal  [Select][+][-]

1.  try
2.  
3.  
4.           try
5.              // do something with a.
6.           finally
7.             c.free; //Now after use clean up the instance
8.           end;
9.  
10.  
11.  
12.         a:=1;
13.         b:=0;
14.         a :=a div b;
15.      except
16.          writeln('division by zero');
17.      end;              
18.  

What the inhibitor would be like this

Code: Pascal  [Select][+][-]

1.    c:=Tobject.create;
2.      try
3.  
4.  
5.        //   try     remove this line
6.              // do something with a.
7.           finally
8.             c.free; //Now after use clean up the instance
9.        //   end;  remove this line
10.  
11.  
12.  
13.         a:=1;
14.         b:=0;
15.         a :=a div b;
16.      except
17.          writeln('division by zero');
18.      end;
19.  

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Title: Re: About the FPC feature
Post by: Thaddy on April 14, 2019, 11:00:58 am

No. try's are separate blocks and need their own try and end. Look at my examples. You can not short-cut by leaving either a try or an end out! My examples are correct.

Title: Re: About the FPC feature
Post by: nouzi on April 14, 2019, 11:11:02 am

@Thaddy thank
It was just a suggestion

Title: Re: About the FPC feature
Post by: Thaddy on April 14, 2019, 11:21:52 am

The reason is they are syntactically different things.