On 20.03.2015 21:18, vfclists . wrote:
On 20 March 2015 at 19:34, Sven Barth <pascaldra...@googlemail.com
<mailto:pascaldra...@googlemail.com>> wrote:
Am 20.03.2015 19:19 schrieb "vfclists ." <vfcli...@gmail.com
<mailto:vfcli...@gmail.com>>:
>
>
>
> On 20 March 2015 at 18:01, leledumbo <leledumbo_c...@yahoo.co.id
<mailto:leledumbo_c...@yahoo.co.id>> wrote:
>>
>> > Where is the 'write' function defined and how is it different
from
>> 'writeln'?
>> >
>> > I can see a lot of fpc_writeXXX and other xxxxWrite functions,
but no
>> > 'write' itself
>>
>> those fpc_writeXXX ARE the actual write. Write(Ln) is NOT a
function as like
>> others whose implementation you can clearly see. It's rather a
command for
>> the compiler to translate to the correct fpc_writeXXX call. So,
if you:
>>
>> WriteLn(123,' is an integer');
>>
>> the compiler will translate it to:
>>
>> fpc_write_text_shortint(123);
>> fpc_write_text_shortstring('is an integer');
>> fpc_writeln_end;
>>
>> The same case applies to Read(Ln). AFAIK Pascal's I/O is part of the
>> language, not the RTL.
>>
>>
>
> Where does the output go? Is it for stdout, strderr or the console?
It depends.
Write('foobar');
Will write to whatever Textfile is contained in Output and
Write(xyz, 'foobar');
Will write to the xyz Textfile. And these Textfiles can basically be
anything. By default Output simply writes to StdOut (there's also a
variable for StdErr, but I have forgotten how it's called...), but
you could also use an implementation that writes to a TStream or one
which uses sockets. It's quite flexible...
Regards,
Sven
How do you ensure own implementation overrides the system's
implementation, does the compiler take care of that automatically, or
will you have to name your function differently?
There is no need to ensure that. Here is an example:
=== code begin ===
var
f, oldout: TextFile;
begin
Writeln('Hello Output as StdOut');
oldout := Output;
Assign(Output, 'test.txt');
Rewrite(Output);
Writeln('Hello Output as file');
Close(f);
Output := oldout;
Writeln('Hello Output as StdOut again');
end.
=== code end ===
To see how such a TextFile is implemented you can take a look at unit
StreamIO which is part of FPC's units.
(Though I wonder why "Assign(f, 'test.txt'); Output := f; Writeln('Hello
Output as file');" does not work :/ )
Regards,
Sven
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