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From: Bonita Montero <Bonita.Montero@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: how copy file on linux?
Date: Fri, 28 Jun 2024 20:15:20 +0200
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I tried to implement that in C++. Unfortunately an error branch of the
code is taken. What Do I have to change ?

bool CopyFileA( char const *from, char const *to, bool overwrite )
{
	struct stat attrFrom, attrTo;
	if( stat( from, &attrFrom ) )
		return false;
	if( !overwrite && !stat( to, &attrTo ) && errno != ENOENT )
		return false;
	union ndi { char c; };
	vector<char> buf( attrFrom.st_size >= 0x100000 ? 0x100000 : 
attrFrom.st_size );
	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;
		}
		if( write( toFile, buf.data(), n ) )
			return false;
	}
	closeTo();
	utimbuf utb;
	utb.actime = attrFrom.st_atime;
	utb.modtime = attrFrom.st_mtime;
	if( utime( to, &utb ) )
		return false;
	if( chmod( to, attrFrom.st_mode ) )
		return false;
	if( chown( to, attrFrom.st_uid, attrFrom.st_gid ) && errno != EACCES )
		return false;
	delTo.disable();
	return to;
}

If everything works fine at last I'll make a C-rewrite.