What’s the use case for formatting monetary values with a *system-dependent* currency symbol

currencyformattinginternationalizationlanguage-agnosticlocalization

Many high-level programming languages have built-in features to format a number with a system-dependent currency symbol:

-- Outputs $100.00 (en-US) or € 100,00 (de-AT)

Console.WriteLine(100.ToString("C"));  // C#
? FormatCurrency(100)                  ' VBA
...

I've been developing business software for more than 20 years, and I've not yet found a single use case for this feature.

The thing is: $ 100 is a completely different amount of money than € 100. If I store 100 in a database field and just "format the value as currency", the user will get a different amount of money depending on their system setting.

Even if I always override the locale, that does not necessarily mean that the currency symbol will stay constant: de-AT (together with a lot of other locales) switched from ATS to € about 20 years ago. In that case, the amount of money displayed would not only vary by locale but also by operating system patch level.

What am I missing? For which use case is this feature actually useful?

Best Answer

Is there a use-case for build-in currency formatting?

Basically, with currencies you have two ways of working:

  • in a currency-aware environment, where people register amount sometimes in local and sometimes in foreign currency: you will never use the default built-in feature. Instead you’ll store a currency amount and a currency code.
  • in a currency-neutral environment. Believe it or not, most private people and most small businesses around the world work only with one local currency, which happens to be the currency configured in their OS settings and never changes. Using the build-in formatting then takes advantage of this fact, and use OS configuration instead of forcing you to add your own configuration step in your software for this. By the way, this formatting has generally also the advantage of using the right decimal and thousand separators.

So yes, there is a use-case for this feature.

But with limitations

This being said, I’m not sure that this standard feature works well and out of the box and in a portable way with:

  • currencies that are expected to be displayed with a different number of decimals than the usual two (such as JPY which are usually shown with no decimals at all, or KWD which take 3 decimals) (if you know, please comment)
  • local financial usages of showing negative amounts either with a minus, or as a positive number between brackets
  • other practical usages, such as showing the currency symbol to the left (US, UK) or to the right (FR, DE) of the amount.

Although OSes may handle these rather well (e.g.: Windows, macOS), the OS independent programming language implementations are sometimes full of surprises and missing flexibility, which could limit the use-case of this feature, but for other reasons.

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