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kate
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 Posted: Sat Feb 05, 2005 8:18 pm Post subject: sizeof |
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salve.
per favore rispondete alla mia domanda:
Come faccio a ottenere le dimensioni di un file?(con c/c++)
risp presto
grazie
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Gianni Mariani
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| Posted: Sat Feb 05, 2005 10:22 pm Post subject: Re: sizeof |
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kate wrote:
| Quote: | salve.
per favore rispondete alla mia domanda:
Come faccio a ottenere le dimensioni di un file?(con c/c++)
|
// get length of file:
ifstream file;
file.open( "file.nome", ios::binary );
file.seekg( 0, ios::end );
int length = file.tellg();
?
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Jack Klein
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Alex Vinokur
Guest
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| Posted: Sun Feb 06, 2005 9:54 am Post subject: Re: sizeof |
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"Jack Klein" <jackklein (AT) spamcop (DOT) net> wrote
| Quote: | On Sat, 05 Feb 2005 14:22:52 -0800, Gianni Mariani
[email]gi2nospam (AT) mariani (DOT) ws[/email]> wrote in comp.lang.c++:
kate wrote:
salve.
per favore rispondete alla mia domanda:
Come faccio a ottenere le dimensioni di un file?(con c/c++)
// get length of file:
ifstream file;
file.open( "file.nome", ios::binary );
file.seekg( 0, ios::end );
int length = file.tellg();
Not guaranteed to be correct, although it works on most platforms.
|
What exactly can be incorrect?
--
Alex Vinokur
email: alex DOT vinokur AT gmail DOT com
http://mathforum.org/library/view/10978.html
http://sourceforge.net/users/alexvn
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Rolf Magnus
Guest
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| Posted: Sun Feb 06, 2005 10:59 am Post subject: Re: sizeof |
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Alex Vinokur wrote:
| Quote: |
"Jack Klein" <jackklein (AT) spamcop (DOT) net> wrote in message
news:0gpb01hntrr85iefk0cqe6b945ecpsjflq (AT) 4ax (DOT) com...
On Sat, 05 Feb 2005 14:22:52 -0800, Gianni Mariani
[email]gi2nospam (AT) mariani (DOT) ws[/email]> wrote in comp.lang.c++:
kate wrote:
salve.
per favore rispondete alla mia domanda:
Come faccio a ottenere le dimensioni di un file?(con c/c++)
// get length of file:
ifstream file;
file.open( "file.nome", ios::binary );
file.seekg( 0, ios::end );
int length = file.tellg();
Not guaranteed to be correct, although it works on most platforms.
What exactly can be incorrect?
|
The result of trying to seek to the end of a binary file is undefined.
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Alex Vinokur
Guest
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| Posted: Sun Feb 06, 2005 11:14 am Post subject: Re: sizeof |
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"Rolf Magnus" <ramagnus (AT) t-online (DOT) de> wrote
| Quote: | Alex Vinokur wrote:
"Jack Klein" <jackklein (AT) spamcop (DOT) net> wrote in message
news:0gpb01hntrr85iefk0cqe6b945ecpsjflq (AT) 4ax (DOT) com...
On Sat, 05 Feb 2005 14:22:52 -0800, Gianni Mariani
[email]gi2nospam (AT) mariani (DOT) ws[/email]> wrote in comp.lang.c++:
kate wrote:
salve.
per favore rispondete alla mia domanda:
Come faccio a ottenere le dimensioni di un file?(con c/c++)
// get length of file:
ifstream file;
file.open( "file.nome", ios::binary );
file.seekg( 0, ios::end );
int length = file.tellg();
Not guaranteed to be correct, although it works on most platforms.
What exactly can be incorrect?
The result of trying to seek to the end of a binary file is undefined.
|
1. What is a reason for that?
2. Can we have any indication of that?
--
Alex Vinokur
email: alex DOT vinokur AT gmail DOT com
http://mathforum.org/library/view/10978.html
http://sourceforge.net/users/alexvn
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Andrea Laforgia
Guest
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| Posted: Sun Feb 06, 2005 3:58 pm Post subject: Re: sizeof |
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kate ha scritto:
| Quote: | per favore rispondete alla mia domanda:
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Per cortesia, non fare uso del cross-post.
Posta la tua domanda in it.comp.lang.c++ (in italiano), oppure in
comp.lang.c++ (in inglese), se vuoi una risposta relativa al C++, oppure
in it.comp.lang.c (in italiano) o in comp.lang.c (in inglese) se vuoi una
risposta relativa al C.
--
questo articolo e` stato inviato via web dal servizio gratuito
http://www.newsland.it/news segnala gli abusi ad [email]abuse (AT) newsland (DOT) it[/email]
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Cingar
Guest
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| Posted: Mon Feb 07, 2005 10:05 am Post subject: Re: sizeof |
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Gianni Mariani ha scritto:
| Quote: | // get length of file:
ifstream file;
file.open( "file.nome", ios::binary );
file.seekg( 0, ios::end );
int length = file.tellg();
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&, in C:
#include <stdio.h>
FILE * file;
file = fopen("file.name", "rb");
fseek(file, 0, SEEK_END);
long length = ftell(file);
--
Cingar
--
questo articolo e` stato inviato via web dal servizio gratuito
http://www.newsland.it/news segnala gli abusi ad [email]abuse (AT) newsland (DOT) it[/email]
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Default User
Guest
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| Posted: Mon Feb 07, 2005 5:39 pm Post subject: Re: sizeof |
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Cingar wrote:
| Quote: | Gianni Mariani ha scritto:
// get length of file:
ifstream file;
file.open( "file.nome", ios::binary );
file.seekg( 0, ios::end );
int length = file.tellg();
&, in C:
#include
FILE * file;
file = fopen("file.name", "rb");
fseek(file, 0, SEEK_END);
long length = ftell(file);
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Also not guaranteed to work.
http://www.eskimo.com/~scs/C-faq/q19.12.html
Brian
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Cingar
Guest
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| Posted: Mon Feb 07, 2005 6:17 pm Post subject: Re: sizeof |
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Default User ha scritto:
| Quote: | Cingar wrote:
Gianni Mariani ha scritto:
// get length of file:
ifstream file;
file.open( "file.nome", ios::binary );
file.seekg( 0, ios::end );
int length = file.tellg();
&, in C:
#include
FILE * file;
file = fopen("file.name", "rb");
fseek(file, 0, SEEK_END);
long length = ftell(file);
Also not guaranteed to work.
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Of course. As the two code fragments are just different syntactic flavors
for exactly the same stuff, either both are guaranteed to work, or both
aren't. :-)
However, I think this is the best approximation you can have with standard
C and C++ libraries.
IMHO, a solid program should use more reliable non-portable API's, and
leave this approach as the default portable implementation. I.e., the
fseek/ftell implementation could be a pretty good #else in a cascade of
platform-specific #elif's.
--
Cingar
--
questo articolo e` stato inviato via web dal servizio gratuito
http://www.newsland.it/news segnala gli abusi ad [email]abuse (AT) newsland (DOT) it[/email]
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Kronos
Guest
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| Posted: Mon Feb 07, 2005 11:55 pm Post subject: Re: sizeof |
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Su it.comp.lang.c Default User <defaultuserbr (AT) yahoo (DOT) com> ha scritto:
IMHO that FAQ entry is not very clear.
"ftell is not guaranteed to return a byte count except for binary files."
It seems that I _can_ fopen() the file as "b", fseek() to the end and then use
ftell().
That sentence should be something like that:
"ftell is not guaranteed to return a byte count except for binary files,
but in this case you can't fseek to the end of the file since fseek
needn't support SEEK_END on binary streams."
Luca
--
Home: http://kronoz.cjb.net
The trouble with computers is that they do what you tell them,
not what you want.
D. Cohen
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Alex Vinokur
Guest
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| Posted: Tue Feb 08, 2005 5:39 am Post subject: Getting file size using ftell()/tellg() (Was: sizeof) |
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"Default User" <defaultuserbr (AT) yahoo (DOT) com> wrote
| Quote: | Cingar wrote:
Gianni Mariani ha scritto:
// get length of file:
ifstream file;
file.open( "file.nome", ios::binary );
file.seekg( 0, ios::end );
int length = file.tellg();
&, in C:
#include
FILE * file;
file = fopen("file.name", "rb");
fseek(file, 0, SEEK_END);
long length = ftell(file);
Also not guaranteed to work.
http://www.eskimo.com/~scs/C-faq/q19.12.html
[snip] |
1. Did anybody really come across that problem (ftell() or/and tellg() don't return what is expected)?
2. ftell() and tellg() are standard function and method. Why/how can their behavior be undefined if we are correctly using them?
--
Alex Vinokur
email: alex DOT vinokur AT gmail DOT com
http://mathforum.org/library/view/10978.html
http://sourceforge.net/users/alexvn
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Jonathan Turkanis
Guest
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| Posted: Tue Feb 08, 2005 5:49 am Post subject: Re: Getting file size using ftell()/tellg() (Was: sizeof) |
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| Quote: | Also not guaranteed to work.
http://www.eskimo.com/~scs/C-faq/q19.12.html
[snip]
1. Did anybody really come across that problem (ftell() or/and
tellg() don't return what is expected)?
2. ftell() and tellg() are standard function and method. Why/how can
their behavior be undefined if we are correctly using them?
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P.J. Plauger has a good discussion of this in his book on the std C library.
Basically it was one of the compromised that had to be made if the standard was
to apply to non-unix systems. Implementations are allowed to add an arbitrary
number of null characters at the end of a binary file, because on some systems,
at some time, no stronger guarantee could be made.
Seeking to the end of a file and querying the offset does not result in
undefined behavior, however. It's just not guaranteed to give you the result you
want.
Jonathan
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Rolf Magnus
Guest
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| Posted: Tue Feb 08, 2005 11:10 am Post subject: Re: Getting file size using ftell()/tellg() (Was: sizeof) |
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Jonathan Turkanis wrote:
| Quote: | Seeking to the end of a file and querying the offset does not result in
undefined behavior, however.
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Yes, it does. At least with fseek/ftell. From the C standard:
Setting the file position indicator to end-of-file, as with fseek(file, 0,
SEEK_END), has undefined behavior for a binary stream (because of possible
trailing null characters) or for any stream with state-dependent encoding
that does not assuredly end in the initial shift state.
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Fabiano
Guest
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| Posted: Mon Oct 24, 2005 8:38 am Post subject: Re: sizeof |
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Alex Vinokur ha scritto:
| Quote: | "Rolf Magnus" <ramagnus (AT) t-online (DOT) de> wrote
Alex Vinokur wrote:
"Jack Klein" <jackklein (AT) spamcop (DOT) net> wrote in message
news:0gpb01hntrr85iefk0cqe6b945ecpsjflq (AT) 4ax (DOT) com...
On Sat, 05 Feb 2005 14:22:52 -0800, Gianni Mariani
[email]gi2nospam (AT) mariani (DOT) ws[/email]> wrote in comp.lang.c++:
kate wrote:
salve.
per favore rispondete alla mia domanda:
Come faccio a ottenere le dimensioni di un file?(con c/c++)
// get length of file:
ifstream file;
file.open( "file.nome", ios::binary );
file.seekg( 0, ios::end );
int length = file.tellg();
Not guaranteed to be correct, although it works on most platforms.
What exactly can be incorrect?
The result of trying to seek to the end of a binary file is undefined.
1. What is a reason for that?
2. Can we have any indication of that?
What happens if we have no READ privilege on this particular files? Is |
this the issue?
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