Default (computer science)
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- For other uses of the word, see the default disambiguation page.
- "Presets" redirects here. For the electronic band, see The Presets.
A default, in computer science, refers to a setting or value automatically assigned to a computer program or device, outside of user intervention. Such settings are also called presets, especially for electronic devices.
Default values are generally intended to make a device (or control) usable "out of the box". The most likely setting, or at least a usable setting, is typically assigned.
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[edit] Examples
[edit] Computer input panel
One use of default parameters is for initial settings on input panels. For example, the first time a user runs a program it may suggest that the user's delivery address is in the United States. This default might be appropriate if more users of that program were in the US than any other country. If the user selected a new country, that would override the default, and perhaps become the default for the next time the program is used on that computer or by that user. Changing the default for the next run would involve storing user info somewhere, such as in cookies on the user's computer for an Internet application.
If too many people complain that the U.S. default is not politically correct, it can be left unchosen. Then it can eitherr simply left as the top and most convenient choice, or be folded back into alphabetical obscurity, where 95% of users will have to dig it up between United Kingdom and Uzbekhistan.
[edit] TV or computer monitor
A TV or computer monitor typically comes with a button to "restore factory presets". This allows the defaults for brightness, contrast, color, etc., to be returned to the settings recommended by the manufacturer. This button may be used when the settings get badly misadjusted (say by a toddler playing with the controls). Some "fine-tuning" of the settings may still be needed from the factory settings, but they are likely closer to the desired settings than the current random settings.
[edit] When to use computer program defaults
Using defaults involves two goals which sometimes conflict:
- Minimal user interaction should be required. Setting defaults to the most commonly selected options serves this purpose.
- Panel entry errors should be minimized. Using defaults will tend to increase errors, as users may leave incorrect default settings selected. In cases where the value can be verified, this is not a severe problem. For example, the delivery country can be checked against the street address/postal codes and any mismatch can generate an error panel displayed to the user, who will then presumably make the correction.
In cases where there is no clear majority and the results can't easily be verified by other available information, such as the gender of the individual, no default should be offered. Note, however, that some software packages require that default values be supplied.
[edit] Computer language defaults
Most languages in the C-family (but not C itself, as of ISO-C99) allow a function to have default parameters, that are used if the function is called with omitted parameter specifications.
In C and languages based on its syntax, the switch statement (which dispatches among a number of alternatives) can make use of the default keyword to provide a case for when no other case matches.
In Fortran, the INIT parameter on a declaration defines an initial default value for that variable.
