Hungarian notation

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Hungarian notation is a naming convention in computer programming, in which the name of an object indicates its type or intended use. There are two types of Hungarian notation: Systems Hungarian notation and Apps Hungarian notation.

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).

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Systems vs. Apps Hungarian

Where Systems notation and Apps notation differ is in the purpose of the prefixes.

In Systems Hungarian notation, the most common form, the prefix encodes the actual data type of the variable. For example:

  • ulAccountNum : variable is an unsigned long integer
  • szName : variable is a zero-terminated string

Apps Hungarian notation doesn't encode the actual data type but rather, it gives a hint as to what the variable's purpose is, or what it represents.

  • rwPosition : variable represents a row
  • usName : variable represents an unsafe string, which needs to be translated by some function to make it safe (e.g. see Cross site scripting)
  • strName : Variable represents a string containing the name, but does not specify how that string is implemented.

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.

It is possible for code using Apps Hungarian notation to sometimes contain Systems Hungarian when describing variables that are defined solely in terms of their type.

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Relation to sigils

In some programming languages, a similar notation now called sigils is built into the language and enforced by the compiler. For example, in BASIC, name$ names a string and count% names an integer, and in Perl, $name refers to a scalar value while @namelist refers to a list of values. Sigils have the notable advantages over Hungarian notation that they implicitly define the type of the variable without need for redundant declaration, and are also checked by the compiler, preventing omission and misuse.

On the other hand, such systems are in practice less flexible than Hungarian notation, typically defining only a few different types — the lack of an adequate number of different easy-to-remember symbols obstructs more extensive use. In addition, although it has not been done, it is feasible to construct a static-checking tool which could statically verify the presence and correctness of Hungarian prefixes.

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Examples

The mnemonics for pointers and arrays, which are not actual data types, are usually followed by the type of the data element itself:

  • pszOwner : pointer to zero-terminated string
  • rgfpBalances : array of floating-point values

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

Hungarian notation becomes confusing when it is used to represent several properties; this is illustrated in the following example:

It is interesting to note that the .NET Framework, Microsoft's new software development platform, lacks Hungarian notation completely; the .NET Framework Guidelines advise programmers that Hungarian notation is not to be used.

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Origin

The original Hungarian notation was Apps Hungarian, which 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 name Apps Hungarian was coined since the convention was used in the applications division of Microsoft.

Systems Hungarian developed later in the Microsoft Windows development team. Simonyi's paper referred to prefixes used to indicate the "type" of information being stored; the word "type" was misunderstood to mean "data type", and systems of prefixes started to be devised on the basis of this misunderstanding.

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 (although Hungarian is not a consonant-rich language!).

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External links

|      author = Joel Spolsky
| year = 2005-05-11
|         url = http://www.joelonsoftware.com/articles/Wrong.html
|       title = Making Wrong Code Look Wrong
|        work = Joel on Software
|        accessdate = 2005-12-13
|}}

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