Formatting is the process of converting a variable from its native type into a string representation. Anytime you display a DateTime or numeric variables in an ASP.NET page, you are formatting that variable from its native type into some sort of string representation. How a DateTime or numeric variable is formatted depends on the culture settings and the format string. Because dates and numeric values are formatted differently across cultures, the .NET Framework bases its formatting on the specified culture settings. By default, the formatting routines use the culture settings defined on the web server, but you can indicate that a particular culture be used anytime you format. In addition to the culture settings, formatting is also affected by a format string, which spells out the formatting details to apply.

The .NET Framework contains a bounty of format strings. There are standard format strings, which are typically a single letter that applies detailed formatting logic. For example, the "C" format specifier will format a numeric type as a currency value; the "Y" format specifier displays the month name and four-digit year of the specified DateTime value. There are also custom format strings, which display a apply a very specific formatting rule. These custom format strings can be put together to build more intricate formats. For instance, the format string "dddd, MMMM d" displays the full day of the week name followed by a comma followed by the full name of the month followed by the day of the month. For more involved formatting scenarios, where neither the standard or custom format strings cut the mustard, you can always create your own formatting extension methods.

This article explores the standard format strings for dates, times and numbers and includes a number of custom formatting methods I've created and use in my own projects. There's also a demo application you can download that lets you specify a culture and then shows you the output for the standard format strings for the selected culture. Read on to learn more!
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