NAME

unpack - convert binary structure into normal perl variables

SYNOPSIS

unpack TEMPLATE,EXPR

DESCRIPTION

Unpack() does the reverse of pack(): it takes a string representing a structure and expands it out into a list value, returning the array value. (In scalar context, it returns merely the first value produced.) The TEMPLATE has the same format as in the pack() function. Here's a subroutine that does substring:

    sub substr {
        my($what,$where,$howmuch) = @_;
        unpack("x$where a$howmuch", $what);
    }

and then there's

    sub ordinal { unpack("c",$_[0]); } # same as ord()

In addition, you may prefix a field with a %<number> to indicate that you want a <number>-bit checksum of the items instead of the items themselves. Default is a 16-bit checksum. For example, the following computes the same number as the System V sum program:

    while (<>) {
        $checksum += unpack("%16C*", $_);
    }
    $checksum %= 65536;

The following efficiently counts the number of set bits in a bit vector:

    $setbits = unpack("%32b*", $selectmask);

DISCLAIMER

We are painfully aware that these documents may contain incorrect links and misformatted HTML. Such bugs lie in the automatic translation process that automatically created the hundreds and hundreds of separate documents that you find here. Please do not report link or formatting bugs, because we cannot fix per-document problems. The only bug reports that will help us are those that supply working patches to the installhtml or pod2html programs, or to the Pod::HTML module itself, for which I and the entire Perl community will shower you with thanks and praises.

If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.

--Tom Christiansen, Perl Documentation Compiler and Editor

Return to the Perl Documentation Index.
Return to the Perl Home Page.