Dear,

little question when writing to a file 5 "hello" lines (by example)
I would like to know if they are a difference between:

writeln( "hello" ); x5

and:

string[] helloList = [ "hello","hello","hello","hello","hello"];
writeln( helloList.join( newline) );


I mean if one way is more efficient by speed?

bioinfornatics:

> I mean if one way is more efficient by speed?

To be sure of what's faster you often have to write small benchmarks.

In this case this should be good:

import std.stdio, std.array;
void main() {
    writefln("%-(%s\n%)", ["hello"].replicate(5));
}


But if you want speed this is is probably faster:

import core.stdc.stdio: puts;
void main() {
    puts("hello\nhello\nhello\nhello\nhello");
}

Bye,
bearophile

The second is probably faster (with optimizations enabled), because each call to writeln incurs overhead of locking/unlocking the file stream (which is stdout in this case).

If you need to print huge amounts of data, use lockingTextWriter like this:

auto w = stdout.lockingTextWriter;
foreach (i; 0 .. 5) {
    w.put("sometext\n");
    w.formattedwrite("%d\n", some_number);
}

However, std.format.formattedWrite is also relatively slow, so it's better to prepare string representation of an object in a buffer on the stack - say, with snprintf, or your own set of formatting functions - and then put it into the writer.

On Thursday, 7 March 2013 at 10:04:34 UTC, bioinfornatics wrote:
> Dear,
>
> little question when writing to a file 5 "hello" lines (by example)
> I would like to know if they are a difference between:
>
> writeln( "hello" ); x5
>
> and:
>
> string[] helloList = [ "hello","hello","hello","hello","hello"];
> writeln( helloList.join( newline) );
>
>
> I mean if one way is more efficient by speed?

On Thursday, 7 March 2013 at 13:37:56 UTC, lomereiter wrote:
> The second is probably faster (with optimizations enabled), because each call to writeln incurs overhead of locking/unlocking the file stream (which is stdout in this case).
>
> If you need to print huge amounts of data, use lockingTextWriter like this:
>
> auto w = stdout.lockingTextWriter;
> foreach (i; 0 .. 5) {
>     w.put("sometext\n");
>     w.formattedwrite("%d\n", some_number);
> }
>
> However, std.format.formattedWrite is also relatively slow, so it's better to prepare string representation of an object in a buffer on the stack - say, with snprintf, or your own set of formatting functions - and then put it into the writer.
>
> On Thursday, 7 March 2013 at 10:04:34 UTC, bioinfornatics wrote:
>> Dear,
>>
>> little question when writing to a file 5 "hello" lines (by example)
>> I would like to know if they are a difference between:
>>
>> writeln( "hello" ); x5
>>
>> and:
>>
>> string[] helloList = [ "hello","hello","hello","hello","hello"];
>> writeln( helloList.join( newline) );
>>
>>
>> I mean if one way is more efficient by speed?

and if is not stdout but File ?

thanks a lot that is really interesting

On Thursday, 7 March 2013 at 16:12:09 UTC, bioinfornatics wrote:
> On Thursday, 7 March 2013 at 13:37:56 UTC, lomereiter wrote:
>> The second is probably faster (with optimizations enabled), because each call to writeln incurs overhead of locking/unlocking the file stream (which is stdout in this case).
>>
>> If you need to print huge amounts of data, use lockingTextWriter like this:
>>
>> auto w = stdout.lockingTextWriter;
>> foreach (i; 0 .. 5) {
>>    w.put("sometext\n");
>>    w.formattedwrite("%d\n", some_number);
>> }
>>
>> However, std.format.formattedWrite is also relatively slow, so it's better to prepare string representation of an object in a buffer on the stack - say, with snprintf, or your own set of formatting functions - and then put it into the writer.
>>
>> On Thursday, 7 March 2013 at 10:04:34 UTC, bioinfornatics wrote:
>>> Dear,
>>>
>>> little question when writing to a file 5 "hello" lines (by example)
>>> I would like to know if they are a difference between:
>>>
>>> writeln( "hello" ); x5
>>>
>>> and:
>>>
>>> string[] helloList = [ "hello","hello","hello","hello","hello"];
>>> writeln( helloList.join( newline) );
>>>
>>>
>>> I mean if one way is more efficient by speed?
>
> and if is not stdout but File ?
>
> thanks a lot that is really interesting

I only replace write by put and do this:
auto output = File( f.absolutePath().expandTilde(), "w" ).lockingTextWriter();


that build without get an error but at runtime i got:
std.exception.ErrnoException@/env/export/nfs2/cns_prog/opt/gdc/include/d/4.7.2/std/stdio.d(1267):  (Bad file descriptor)

Indeed, that shouldn't be the case. I filed a bug request:

http://d.puremagic.com/issues/show_bug.cgi?id=9661

While it isn't fixed, assign file to a variable so that it doesn't go out of scope.

On Thursday, 7 March 2013 at 16:20:24 UTC, bioinfornatics wrote:
>
> I only replace write by put and do this:
> auto output = File( f.absolutePath().expandTilde(), "w" ).lockingTextWriter();
>
>
> that build without get an error but at runtime i got:
> std.exception.ErrnoException@/env/export/nfs2/cns_prog/opt/gdc/include/d/4.7.2/std/stdio.d(1267):
>  (Bad file descriptor)