pack and unpack are useful tools for generating strings of bytes for interchange and extracting values from such strings respectively. What follows is a table that represents the relevant formats in a convenient form.

Category Type Byte Order Mnemonic
Native Little-Endian (<) Big-Endian (>)
Unsigned C "C" for char
Signed c
Unsigned S S< or v S> or n "S" for short
Signed s s< or v! s> or n!
Unsigned L L< or V L> or N "L" for long
Signed l l< or V! l> or N!
Unsigned Q Q< Q> "Q" for quad
Signed q q< q>
Types Used
By This Build
of perl
UV (unsigned integer) J J< J> "J" is related to "I"
IV (signed integer) j j< j>
NV (floating-point) F F< F> "F" for float
C Types for
This Build
of perl
unsigned char
signed char
unsigned short int S! S!< S!> "S" for short
signed short int s! s!< s!>
unsigned int I! or I I!< or I< I!> or I> "I" for int
signed int i! or i i!< or i< i!> or i>
unsigned long int L! L!< L!> "L" for long
signed long int l! l!< l!>
unsigned long long int
signed long long int
float f f< f> "f" for float
double d d< d> "d" for double
long double D D< D> A bigger double

For the pointers used by this build of perl, you can use the following:

use Config qw( %Config ); use constant PTR_SIZE => $Config{ptrsize}; use constant PTR_PACK_FORMAT => PTR_SIZE == 8 ? 'Q' : PTR_SIZE == 4 ? 'L' : die("Unrecognized ptrsize\n");


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Re: Mini-Tutorial: Formats for Packing and Unpacking Numbers
by xiaoyafeng (Deacon) on Jan 13, 2020 at 06:47 UTC
    Many thanks! It's very useful.

    I am trying to improve my English skills, if you see a mistake please feel free to reply or /msg me a correction