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From: Malcolm McLean <malcolm.arthur.mclean@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: how copy file on linux?
Date: Sat, 29 Jun 2024 00:04:00 +0100
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On 28/06/2024 19:15, Bonita Montero wrote:
> int fromFile = open( from, O_RDONLY | O_NOATIME );
>      if( !fromFile )
>          return false;
>      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.

-- 
Check out my hobby project.
http://malcolmmclean.github.io/babyxrc