Hungarian notation
Hungarian notation is a naming convention in computer programming, in which the name of an object indicates its type and intended use.
It was designed to be language independent, and found its first major use with the BCPL programming language. Because BCPL has no data types other than the machine word, nothing in the language itself helps a programmer remember variables' types. Hungarian notation aims to remedy this by providing the programmer with explicit knowledge of each variable's data type.
In Hungarian notation, a variable name starts with one or more lower-case letters which are mnemonics for the type or purpose of that variable, followed by whatever the name the programmer has chosen; this last part is sometimes distinguished as the given name. The first character of the given name is capitalized to separate it from the type indicators (see also CamelCase).
While the notation always uses initial lower-case letters as mnemonics, it does not prescribe the mnemonics themselves. There are several widely used conventions (see examples below), but any set of letters can be used, as long as they are consistent within a given body of code.
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Similar notations in other programming languages
In some programming languages, a similar notation is built into the language. For example, in BASIC, name$ names a string and count% names an integer, while in FORTRAN, variables beginning with I, J, K, L, M, and N are automatically treated as integers by default. Other computer languages such as Perl deduce type from context, while some like Pascal and Java use strong typing to prevent operations involving incompatible types in the first place.
Examples
- nSize : integer
- cApples : count of items
- dwLightYears : double word
- bBusy : boolean
- fBusy : boolean (flag)
- pFoo : pointer
- szLastName : zero-terminated string
- rgStudents : array, or range
The mnemonics for pointers and arrays, which are not actual data types, are usually followed by the type of the data element itself:
- rgfBalances : array of floating-point values
- pszOwner : pointer to zero-terminated string
While Hungarian notation can be applied to any programming language and environment, it was widely adopted by Microsoft for use with the C language, in particular for Microsoft Windows, and its use remains largely confined to that area. Thus, many commonly-seen constructs of Hungarian notation are specific to Windows:
- hwndFoo : handle to a window
- lpszBar : long pointer to a zero-terminated string
The notation is sometimes extended in C++ to include the scope of a variable, separated by an underscore:
- m_nWheels : member of a class, integer
A humorous example of Hungarian notation is this example: [1]
- a_crszkvc30LastNameCol : constant reference function argument, holding contents of a database column of type varchar(30) called LastName that was part of the table's primary key
Origin
Hungarian notation was invented by Charles Simonyi, a programmer working at Xerox, who later became Chief Architect at Microsoft. The name comes from Simonyi's nation of origin, and was also probably inspired by the name of an unrelated concept, Polish notation. The term Hungarian notation is memorable for many people because the strings of unpronounceable consonants vaguely resemble the consonant-rich orthography of some Eastern European languages.
External links
- Meta-Programming: A Software Production Method. Charles Simonyi, December 1976 (PhD Thesis)
- Charles Simonyi's explanation of Hungarian Notation
- MSDN Windows 98 Conventions and Data Types
- Portland Pattern Repository Wiki discussion
- Making Wrong Code Look Wrong
- HTML version of Doug Klunder's paper