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Math::Currency - Exact Currency Math with Formatting and Rounding

• NAME
• SYNOPSIS
• DESCRIPTION
• Important Note on Input Values
• Output Formatting
• Currency Symbol
• Predefined Locales
• Global Format
• POSIX Locale Global Formatting
• Object Formats
• Format Parameters
• SEE ALSO

NAME

Math::Currency - Exact Currency Math with Formatting and Rounding

SYNOPSIS

 use Math::Currency qw(Money $LC_MONETARY);
 $dollar = Math::Currency->new("$12,345.67");
 $taxamt = $dollar * 0.28;
 # this sets the default format for all objects w/o their own format
 Math::Currency->format( $LC_MONETARY->{EUR} );
 $euro = Money(12345.67);
 $euro_string = Money(12345.67)->bstr();
 # or if you already have a Math::Currency object
 $euro_string = "$euro";

DESCRIPTION

Currency math is actually more closely related to integer math than it is to floating point math. Rounding errors on addition and subtraction are not allowed and division/multiplication should never create more accuracy than the original values. All currency values should round to the closest cent or whatever the local equivalent should happen to be.

All common mathematical operations are overloaded, so once you initialize a currency variable, you can treat it like any number and the module will do the right thing. This module is a thin layer over Math::BigFloat which is itself a layer over Math::BigInt.

Important Note on Input Values

Since the point of this module is to perform currency math and not floating point math, it is important to understand how the initial value passed to new() may have nasty side effects if done improperly. Most of the time, the following two objects are identical:

        $cur1 = new Math::Currency 1000.01;
        $cur2 = new Math::Currency "1000.01";

However, only the second is guaranteed to do what you think it should do. The reason for that lies in how Perl treats bare numbers as opposed to strings. The first new() will receive the Perl-stringified representation of the number 1000.01, whereas the second new() will receive the string ``1000.01'' instead. With most locale settings, this will be largely identical. However, with many European locales (like fr_FR), the first new() will receive the string ``1 000,01'' and this will cause Math::BigFloat to report this as NAN (Not A Number) because of the odd posix driven formatting.

For this reason, it is always recommended that input values be quoted at all times, even if your POSIX locale does not have this unfortunate side effect.

Output Formatting

Each currency value can have an individual format or the global currency format can be changed to reflect local usage. I used the suggestions in Tom Christiansen's PerlTootC to implement translucent attributes. If you have set your locale values correctly, this module will pick up your local settings or US standards if you haven't.

Currency Symbol

The locale definition includes two different Currency Symbol strings: one is the native character(s), like $ or £ or DM; the other is the three character string defined by the ISO4217 specification followed by the normal currency separation character (frequently space). The default behavior is to always display the native CURRENCY_SYMBOL unless a global parameter is set:

    $Math::Currency::use_int = 1; # print the currency symbol text

where the INT_CURR_SYMBOL text will used instead.

Predefined Locales

There are currently four predefined Locale LC_MONETARY formats:

    USD = United States dollars (the default if no locale)
    EUR = One possible Euro format (no single standard, yet)
    GBP = British Pounds Sterling
    JPY = Japanese Yen (with extended ASCII currency character)

These hashes can be retrieved using the optional export $LC_MONETARY, like this:

    $format = $LC_MONETARY->{EUR};

This $format hash can be used to set either object formats (see Object Formats) or can be used to set the package format (see Global Format) that all objects will inherit by default.

Global Format

Global formatting can be changed by setting the package global format like this:

    Math::Currency->format($LC_MONETARY->{USD});

POSIX Locale Global Formatting

In addition to the four predefined formats listed above, you can also use the POSIX monetary format for a locale which you are not currently running (e.g. for a web site). You can set the global monetary format in effect at any time by using:

    use POSIX qw( locale_h );
    setlocale(LC_ALL,"en_GB");   # some locale alias
    Math::Currency->initialize;  # reinitialize global format

If you don't want to always have to remember to reinitialize the POSIX settings when you switch locales, you can set the global parameter:

        $Math::Currency::always_init = 1;

and every single time a M::C object is printed, the global $FORMAT will be updated to the locale current at that time. This may be a performance hit. It would be better if you followed the first method of manually updating the global format immediately after you reset the locale.

NOTE: This function will reset only the global format and will not have effect on objects created with their own overridden formats, even if they were originally based on the global format.

NOTE 2: You must have all the locale files in question already loaded; the list reported by `locale -a` is not always a reliable judge of what files you might actually have installed. If you try and set a nonexistant locale, or set the same locale as is already active, the module will silently retain the current locale settings.

Object Formats

Any object can have it's own format different from the current global format, like this:

    $pounds  = Math::Currency->new(1000, $LC_MONETARY->{GBP});
    $dollars = Math::Currency->new(1000); # inherits default US format
    $dollars->format( $LC_MONETARY->{USD} ); # explicit object format

Format Parameters

The format must contains all of the commonly configured LC_MONETARY Locale settings. For example, these are the values of the default US format (with comments): { INT_CURR_SYMBOL => 'USD', # ISO currency text CURRENCY_SYMBOL => '$', # Local currency character MON_DECIMAL_POINT => '.', # Decimal seperator MON_THOUSANDS_SEP => ',', # Thousands seperator MON_GROUPING => '3', # Grouping digits POSITIVE_SIGN => '', # Local positive sign (see below) NEGATIVE_SIGN => '-', # Local negative sign (see below) INT_FRAC_DIGITS => '2', # Default Intl. precision FRAC_DIGITS => '2', # Local precision P_CS_PRECEDES => '1', # Currency symbol location P_SEP_BY_SPACE => '0', # Space between Currency and value N_CS_PRECEDES => '1', # Negative version of above N_SEP_BY_SPACE => '0', # Negative version of above P_SIGN_POSN => '1', # Position of positive sign (see below) N_SIGN_POSN => '1', # Position of negative sign (see below) }

Each of the formatting parameters can be individually changed at the object or class (global) level; if an object is currently sharing the global format, all the global parameters will be copied prior to setting the overrided parameters. For example:

    $dollars = Math::Currency->new(1000); # inherits default US format
    $dollars->format('CURRENCY_SYMBOL',' Bucks'); # now has its own format
    $dollars->format('P_CS_PRECEDES',0); # now has its own format
    print $dollars; # displays as "1000 Bucks"

Or you can also set individual elements of the current global format:

   Math::Currency->format('CURRENCY_SYMBOL',' Bucks'); # global changed

The [NP]_SIGN_POSN parameter determines how positive and negative signs are displayed. [NP]_CS_PRECEEDS determines where the currency symbol is shown. [NP]_SEP_BY_SPACE determines whether the currency symbol cuddles the value or not. The following table shows the relationship between these three parameters:

                                               p_sep_by_space
                                         0          1          2

 p_cs_precedes = 0   p_sign_posn = 0    (1.25$)    (1.25 $)   (1.25 $)
                     p_sign_posn = 1    +1.25$     +1.25 $    +1.25 $
                     p_sign_posn = 2     1.25$+     1.25 $+    1.25$ +
                     p_sign_posn = 3     1.25+$     1.25 +$    1.25+ $
                     p_sign_posn = 4     1.25$+     1.25 $+    1.25$ +

 p_cs_precedes = 1   p_sign_posn = 0   ($1.25)   ($ 1.25)   ($ 1.25)
                     p_sign_posn = 1   +$1.25    +$ 1.25    + $1.25
                     p_sign_posn = 2    $1.25+    $ 1.25+     $1.25 +
                     p_sign_posn = 3   +$1.25    +$ 1.25    + $1.25
                     p_sign_posn = 4   $+1.25    $+ 1.25    $ +1.25

(the negative variants are similar).

=head1 AUTHOR

John Peacock <jpeacock@rowman.com>

SEE ALSO

 perl(1).
 perllocale
 Math::BigFloat
 Math::BigInt

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