Newbie question on an I/O loop

[Jay Daniels]

I got a question that's puzzling me. Am new to Ruby but programming for
decades. Here's the problem. This apparently simple loop reads 396 bytes
of a file and no more. The actual file is 1.5KB and I can display it
easily in a hex dumper. The bytes Ruby has read are all correct. It just
seems to stop after 396 bytes. Any idea what's wrong or where I should
be looking?

Many thanks in advance,

JK Daniels

if ARGV[0] == nil
puts( "\n" + $help )
else
i = 0
tfm = File.open( ARGV[0] )
tfm.each_byte{ |c| i = i + 1; printf( "%d: %X\n", i, c ) }
if tfm.eof
puts "at eof" else puts "not at eof"
end
end

<<< end code <<<

This outputs the first 396 bytes and then state it's at EOF. If it makes
any difference, the last three bytes it reads are (all hex): C0 A4 00
and the next three (unread) bytes in the file are: 1A C0 B5

 

[Steven R.]

I got a question that's puzzling me. Am new to Ruby but programming for
decades. Here's the problem. This apparently simple loop reads 396 bytes
of a file and no more. The actual file is 1.5KB and I can display it
easily in a hex dumper. The bytes Ruby has read are all correct. It just
seems to stop after 396 bytes. Any idea what's wrong or where I should
be looking?

Many thanks in advance,

JK Daniels

if ARGV[0] == nil
puts( "\n" + $help )
else
i = 0
tfm = File.open( ARGV[0] )
tfm.each_byte{ |c| i = i + 1; printf( "%d: %X\n", i, c ) }
if tfm.eof
puts "at eof" else puts "not at eof"
end
end

<<< end code <<<

This outputs the first 396 bytes and then state it's at EOF. If it makes
any difference, the last three bytes it reads are (all hex): C0 A4 00
and the next three (unread) bytes in the file are: 1A C0 B5

I tested this on a file that was 29,184 bytes - it worked fine.

Could it be something in your data or environment?

Sorry I couldn't be of more help.

 

[ts]

J> and the next three (unread) bytes in the file are: 1A C0 B5
^^^
moulon% /usr/bin/ruby -e 'p "%c" % 0x1A'
"\032"
moulon%


it's Control-Z, use "rb" to open the file


p.s.:

moulon% ruby -e 'p "%c" % 0x1A'
-e:1: [BUG] Segmentation fault
ruby 1.9.0 (2006-07-14) [i686-linux]

Aborted
moulon%


Guy Decoux

 

[Jay Daniels]

Thank you Guy, Steven, and Robert for solving the problem. I appreciate
it. Never occurred to me it could be a control-z problem. Robert, thanks
especially for showing the same code using typical Ruby metaphors. This
also helps a lot.

J K Daniels

J> and the next three (unread) bytes in the file are: 1A C0 B5
^^^
moulon% /usr/bin/ruby -e 'p "%c" % 0x1A'
"\032"
moulon%


it's Control-Z, use "rb" to open the file


p.s.:

moulon% ruby -e 'p "%c" % 0x1A'
-e:1: [BUG] Segmentation fault
ruby 1.9.0 (2006-07-14) [i686-linux]

Aborted
moulon%


Guy Decoux