Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Lew Pitcher <lew.pitcher@digitalfreehold.ca>
Newsgroups: comp.lang.c
Subject: Re: how copy file on linux?
Date: Fri, 28 Jun 2024 23:27:49 -0000 (UTC)
Organization: A noiseless patient Spider
Lines: 55
Message-ID: <v5ngtl$3ehss$3@dont-email.me>
References: <v5huk1$2anbd$1@dont-email.me>
	<v5mujo$3f10p$1@raubtier-asyl.eternal-september.org>
	<v5nfh0$3i4n8$1@dont-email.me> <v5ngp0$3ehss$2@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Injection-Date: Sat, 29 Jun 2024 01:27:50 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="a6c2d2db8ef704f1aabece0e415918ba";
	logging-data="3622812"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/7minrkKleuYxPcScNfTUvr5/3pzmmQYA="
User-Agent: Pan/0.139 (Sexual Chocolate; GIT bf56508
 git://git.gnome.org/pan2)
Cancel-Lock: sha1:P20CY+Aos5EQGVGKRMHN2YBBASw=
Bytes: 3028

Oops. missed part of my edit. See unquoted line below

On Fri, 28 Jun 2024 23:25:20 +0000, Lew Pitcher wrote:

> On Sat, 29 Jun 2024 00:04:00 +0100, Malcolm McLean wrote:
> 
>> On 28/06/2024 19:15, Bonita Montero wrote:
>>> int fromFile = open( from, O_RDONLY | O_NOATIME );
>>>      if( !fromFile )
>>>          return false;
> 
> open() returns -1 on failure, and some non-negative number
> on success. That non-negative number /can be/ 0 and still
> be a valid success value.
> 
> The above test /will not/ detect an open() failure, as !(-1) == 0
> However, the above /will/ falsely call
a FAILURE (and return a "false" from the function)
> a valid open() that returns
> fd 0 (slim chance unless you've previously closed stdin).
> 
> 
>>>      invoke_on_destruct closeFrom( [&] { close( fromFile ); } );
>>>  //    int toFile = open( to, O_CREAT );
>>>  //    if( !toFile )
>>>  //        return false;
>>>      invoke_on_destruct closeTo( [&] { close( toFile ); } );
>>> //     invoke_on_destruct delTo( [&] { unlink( to ); } );
>>>      for( int64_t remaining = attrFrom.st_size; remaining > 0; remaining 
>>> -= 0x100000 )
>>>      {
>>>          size_t n = (size_t)(remaining >= 0x100000 ? 0x100000 : remaining);
>>>          buf.resize( n );
>>>          if( read( fromFile, buf.data(), n ) )
>>>          {
>>>              // this branch is taken
>>>              cout << strerror( errno ) << endl;
>>>              return false;
>>>          }
>> 
>> So it claims the file opens, then won't read it?
>> 
>> Check the call. Is 0 the success return?
>> 
>> Then I must admit I'm stumped. "to" doesn't alias "from" I suppose?
>> 
>> I'd also wonder if somehow the C++ compiler has invoked the on destruct 
>> code, and closed the file.




-- 
Lew Pitcher
"In Skills We Trust"