Which is faster? - Programming Languages

On 10 Nov, 10:28, Bo Yang <struggl...@gmail.com> wrote:
[color=blue]
>    I am figuring when I want to read a line (maybe 2M bytes long) from
> a file. Which method is faster in C++?
>
> 1. for(; getchar()
> 2. getline(file, string)[/color]

well you could just time 'em. I'd bet on 2 if I were a betting man
because it involves less function calls.

Note: as written 1 never terminates...

You might consider fread().


--
Nick Keighley

Bo Yang wrote:[color=blue]
> Hi,
> I am figuring when I want to read a line (maybe 2M bytes long) from
> a file. Which method is faster in C++?
>
> 1. for(; getchar()
> 2. getline(file, string)[/color]

Why not try it out? On as many different OSes, files, and hardware as
you can find.

Looking at it logically, it seems to me #2 should be faster, as
'getline' implementations usually are aware of read buffering. If you
want to write your own version and it should be fast, just read 3 Mb of
data in one huge block (usually --again-- that's the fastest way to read
any data) and find the line end in there.

[Jw]

Nick Keighley wrote:[color=blue]
> On 10 Nov, 10:28, Bo Yang <struggl...@gmail.com> wrote:
>[color=green]
>> I am figuring when I want to read a line (maybe 2M bytes long) from
>> a file. Which method is faster in C++?
>>
>> 1. for(; getchar()
>> 2. getline(file, string)[/color]
>
> well you could just time 'em. I'd bet on 2 if I were a betting man
> because it involves less function calls.[/color]

On my machine, 2 involves more function calls.
The C implementation on my machine,
implements getchar as a macro.

--
pete

On Nov 10, 7:56 pm, "[Jongware]" <so...@no.spam.net> wrote:[color=blue]
> Bo Yang wrote:[color=green]
> > Hi,
> >    I am figuring when I want to read a line (maybe 2M bytes long) from
> > a file. Which method is faster in C++?[/color]
>[color=green]
> > 1. for(; getchar()
> > 2. getline(file, string)[/color]
>
> Why not try it out? On as many different OSes, files, and hardware as
> you can find.
>
> Looking at it logically, it seems to me #2 should be faster, as
> 'getline' implementations usually are aware of read buffering. If you
> want to write your own version and it should be fast, just read 3 Mb of
> data in one huge block (usually --again-- that's the fastest way to read
> any data) and find the line end in there.[/color]

Yeah, thank you for all your replies.

Regards!
Bo

Nick Keighley said:
[color=blue]
> On 10 Nov, 10:28, Bo Yang <struggl...@gmail.com> wrote:
>[color=green]
>> I am figuring when I want to read a line (maybe 2M bytes long) from
>> a file. Which method is faster in C++?
>>
>> 1. for(; getchar()
>> 2. getline(file, string)[/color]
>
> well you could just time 'em. I'd bet on 2 if I were a betting man
> because it involves less function calls.[/color]

Fewer, man! fewer! :-)

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -http://www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

Bo Yang wrote:[color=blue]
>
> I am figuring when I want to read a line (maybe 2M bytes long)
> from a file. Which method is faster in C++?
>
> 1. for(; getchar()
> 2. getline(file, string)[/color]

A 2 Megabyte line seems excessive, and I greatly doubt you will be
able to reserve a suitable buffer outside the malloc system. I
suggest you rethink the application.

--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home.att.net>
Try the download section.

On Nov 11, 7:19 am, CBFalconer <cbfalco...@yahoo.com> wrote:[color=blue]
> Bo Yang wrote:
>[color=green]
> > I am figuring when I want to read a line (maybe 2M bytes long)
> > from a file. Which method is faster in C++?[/color]
>[color=green]
> > 1. for(; getchar()
> > 2. getline(file, string)[/color]
>
> A 2 Megabyte line seems excessive, and I greatly doubt you will be
> able to reserve a suitable buffer outside the malloc system.  I
> suggest you rethink the application.[/color]

And for another words, how does getline implemented inside the
library? Does it allocate some buffer and read the file and then
detect a '\n' in the buffer?

Thanks!

Regards!
Bo