File IO problem

File IO problem

[prashna]

Hi all,
Pls have a look at the following code

with text_Io;
use text_io;
Procedure FILE_IO_DEMO is
   FILE_I, FILE_O : FILE_TYPE;
   S : STRING(1..80);
   Len : Integer;
begin
   open (FILE_I, IN_FILE,"junk.txt");
   create(FILE_O, OUT_FILE, "output.txt");
   while END_OF_FILE(FILE_I) loop
      GET_LINE(FILE_I, S, Len);
      PUT_LINE(S(1..LEN));
      PUT_LINE(FILE_O,S(1..Len));
   end loop;
end;

The contents of the file junk.txt is
lafeosbv 
qfowep p4gowb
hfwevwpbv

The program is creating output.txt but it contents are nil.

Pls let me know if I am doing wrong.Any help will be appriciated.

Re: File IO problem

[Grein, Christoph]

> with text_Io;
> use text_io;
> Procedure FILE_IO_DEMO is
>    FILE_I, FILE_O : FILE_TYPE;
>    S : STRING(1..80);
>    Len : Integer;
> begin
>    open (FILE_I, IN_FILE,"junk.txt");
>    create(FILE_O, OUT_FILE, "output.txt");
>    while END_OF_FILE(FILE_I) loop
          ^   <-- insert here
         not
>       GET_LINE(FILE_I, S, Len);
>       PUT_LINE(S(1..LEN));
>       PUT_LINE(FILE_O,S(1..Len));
>    end loop;
> end;
> 
> The contents of the file junk.txt is
> lafeosbv 
> qfowep p4gowb
> hfwevwpbv
> 
> The program is creating output.txt but it contents are nil.
> 
> Pls let me know if I am doing wrong.Any help will be appriciated.

Re: File IO problem

[Martin Dowie]

"prashna" <vashwath@rediffmail.com> wrote in message
news:d40d7104.0212052227.3aaa570a@posting.google.com...
>    while END_OF_FILE(FILE_I) loop

You'll probably want a second look at this line.

Re: File IO problem

[Jeffrey Carter]

prashna wrote:
> Hi all,
> Pls have a look at the following code
> 
> with text_Io;
> use text_io;
> Procedure FILE_IO_DEMO is
>    FILE_I, FILE_O : FILE_TYPE;
>    S : STRING(1..80);
>    Len : Integer;
> begin
>    open (FILE_I, IN_FILE,"junk.txt");
>    create(FILE_O, OUT_FILE, "output.txt");
>    while END_OF_FILE(FILE_I) loop
>       GET_LINE(FILE_I, S, Len);
>       PUT_LINE(S(1..LEN));
>       PUT_LINE(FILE_O,S(1..Len));
>    end loop;
> end;
> 
> The contents of the file junk.txt is
> lafeosbv 
> qfowep p4gowb
> hfwevwpbv
> 
> The program is creating output.txt but it contents are nil.

This is an example of why, in 1980, Ichbiah, Barnes, & Firth recommended 
not using while loops. It is natural to think about the exit condition 
for a loop, but a while loop requires its opposite, the continuation 
condition.

Had this been written with an exit:

loop
    exit when End_Of_File (File_I);

there would not have been a problem.

-- 
Jeff Carter
"From this day on, the official language of San Marcos will be Swedish."
Bananas