On 8 April 2010 06:30, Raymond Wan <r....@aist.go.jp> wrote:
>
> Hi all,
>
> I would like to read in a binary file and extract the 4-byte ints from it.
> Under Linux, something like "od -t uI". I got it working as follows:
>
>
> my $buffer = <STDIN>;
> my @buffer = split //, $buffer;
> for (my $i = 0; $i < length ($buffer); $i += 4) {
> print unpack ('I', $buffer[$i].$buffer[$i + 1].$buffer[$i + 2].$buffer[$i +
> 3]), "\n";
> }
Are you sure you want to read using the <> line input operator?
Consider the file (as a hexdump):
00000000 000a0000
There are 8 bytes, corresponding to 2 4-byte ints. The two 4-byte ints
have values 0 and 10*256*256 = 655360 (assuming big endian). But if 0a
happens to be the value of a newline char (as it is under ascii and
utf-8) and you read line-by-line you get two lines:
"\0\0\0\0\0"
and
"\0\0"
which your program will interpret as three ints of values (0,0,0), and
not 2 ints with values (0,655360).
Use 'read' instead (perldoc -f read) to read binary data.
Phil
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