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Revision as of 13:09, 6 December 2011
 | This article needs additional citations for verification. (December 2007) |
Text sometimes exhibits case sensitivity; that is, words can differ in meaning based on differing use of uppercase and lowercase letters. Words with capital letters do not always have the same meaning when written with lowercase letters. For example, Bill is the first name of former U.S. president William Clinton, who could sign a bill (which is a proposed law that was approved by Congress). And a Polish person can use polish to clean something. In food, the Calorie, with a capital C, is sometimes used to denote 1000 calories of energy.
In computers, some examples of usually case sensitive data are
- usernames
- passwords
- filenames
- tags
- commands
- variable names
- searching for a text string within electronic text
Some computer languages are case-sensitive (Java, C++, C#, C,[1] Ruby[2] and XML). Others are case-insensitive (i.e., not case-sensitive), such as most BASICs (an exception being BBC BASIC), SQL[3] and Pascal. There are also languages, such as Haskell and Prolog, in which the capitalization of an identifier encodes information about its semantics.
It takes more work for a program to ignore case when comparing data, depending on the data being compared. Usually it suffices in text coded in character sets like ASCII or EBCDIC to merely convert the comparand and the data temporarily to one case and then compare. However, it becomes far more challenging in a multi-lingual environment, e.g., using Unicode, since case-conversion rules differ between some languages.
Case-insensitive operations are sometimes said to fold case, from the idea of folding the character code table so that upper- and lower-case letters coincide. The alternative smash case is more likely to be used by someone that considers this behaviour a misfeature or in cases wherein one case is actually permanently converted to the other.
In Unix filesystems filenames are usually case sensitive. Current Windows filesystems (VFAT, FAT32, NTFS) are not case sensitive (there cannot be a readme.txt and a Readme.txt in the same folder) but case preserving, i.e. remembering the case of the letters. The original FAT12 was case insensitive.
References
- ^ Kernighan, Brian W. (1978). "Chapter 2: Types, Operators and Expressions". The C Programming Language (1st ed.). Englewood Cliffs, NJ: Prentice Hall. p. 33. ISBN 0-13-110163-3.
{{cite book}}: Unknown parameter|coauthors=ignored (|author=suggested) (help); Unknown parameter|month=ignored (help) - ^ Matsumoto, Yukihiro (2002). "Chapter 2: Language Basics". Ruby in a nutshell (1st ed.). O'Reilly Media. p. 9. ISBN 0-596-00214-9.
{{cite book}}: Unknown parameter|month=ignored (help) - ^ Although one can explicitly set a single database or column collation to be case-sensitive
how did john marshall esablished the supreme courts?