Definitions

Hungarian notation

Hungarian notation

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

Hungarian notation 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 three 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 can be capitalised to separate it from the type indicators (see also CamelCase). Otherwise the case of this character denotes scope.

History

The original Hungarian notation, which would now be called Apps Hungarian, was invented by Charles Simonyi, a programmer who worked at Xerox PARC circa 1972-1981, and who later became Chief Architect at Microsoft.

The notation is an ironic reference to Simonyi's nation of origin; Hungarian people's names are "reversed" compared to most other European names; the family name precedes the given name. For example, the anglicized name "Charles Simonyi" in Hungarian was originally "Simonyi Károly". In the same way the type name precedes the "given name" in Hungarian notation rather than the more natural, to most Europeans, Smalltalk "type last" naming style e.g. aPoint and lastPoint. This latter naming style was most common at Xerox PARC during Simonyi's tenure there. It may also be inspired by play on the name of an almost entirely 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. His proposal was largely concerned with decorating identifier names based upon the semantic information of what they store (in other words, the variable's purpose), consistent with Apps Hungarian. However, his suggestions were not entirely distinct from what became known as Systems Hungarian, as some of his suggested prefixes contain little or no semantic information. (See below for examples.)

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 despite the fact that Hungarian is a Finno-Ugric language, and unlike Slavic languages is rather richer in vowels. For example the zero-terminated string prefix "sz" is also a letter in the Hungarian alphabet (cf. the Eszett 'ß' from German).

Systems vs. Apps Hungarian

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

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

  • lAccountNum : variable is a long integer ("l");
  • arru8NumberList : variable is an array of unsigned 8-bit integers ("arru8");
  • szName : variable is a zero-terminated string ("sz"); this was one of Simonyi's original suggested prefixes.

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 ("rw");
  • usName : variable represents an unsafe string ("us"), which needs to be "sanitized" before it is used (e.g. see code injection and cross-site scripting for examples of attacks that can be caused by using raw user input)
  • strName : Variable represents a string ("str") containing the name, but does not specify how that string is implemented.

Most, but not all, of the prefixes Simonyi suggested are semantic in nature. The following are examples from the original paper:

  • pX is a pointer to another type X; this contains very little semantic information.
  • d is a prefix meaning difference between two values; for instance, dY might represent a distance along the Y-axis of a graph, while a variable just called y might be an absolute position. This is entirely semantic in nature.
  • sz is a null- or zero-terminated string. In C, this contains some semantic information because it's not clear whether a variable of type char* is a pointer to a single character, an array of characters or a zero-terminated string.
  • w marks a variable that is a word. This contains essentially no semantic information at all, and would probably be considered Systems Hungarian.
  • b marks a byte, which in contrast to w might have semantic information, because in C the only byte-sized data type is the char, so these are sometimes used to hold numeric values. This prefix might clear ambiguity between whether the variable is holding a value that should be treated as a letter (or more generally a character) or a number.

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.

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 variable while @namelist refers to an array. 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 adequate 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.

Examples

  • bBusy : boolean
  • cApples : count of items
  • dwLightYears : double word (systems)
  • fBusy : boolean (flag)
  • nSize : integer (systems) or count (application)
  • iSize : integer (systems) or index (application)
  • fpPrice: floating-point
  • dbPi : double (systems)
  • pFoo : pointer
  • rgStudents : array, or range
  • szLastName : zero-terminated string
  • u32Identifier : unsigned 32-bit integer (systems)
  • stTime : clock time structure
  • fnFunction : function name

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. This extension is often also used without the Hungarian type-specification:

  • g_nWheels : member of a global namespace, integer
  • m_nWheels : member of a structure/class, integer
  • m_wheels : member of a structure/class
  • s_wheels : static member of a class
  • _wheels : local variable

Advantages of Systems Hungarian

(Some of these apply to Systems Hungarian only.) Supporters argue that the benefits of Hungarian Notation include:

  • The variable type can be seen from its name
  • The formatting of variable names may simplify some aspects of code refactoring
  • Multiple variables with similar semantics can be used in a block of code: dwWidth, iWidth, fWidth, dWidth
  • Variable names can be easy to remember from knowing just their types.
  • It leads to more consistent variable names
  • Deciding on a variable name can be a mechanical, and thus quick, process
  • Inappropriate type casting and operations using incompatible types can be detected easily while reading code
  • Useful with string based languages where numerics are strings (Tcl for example)
  • In Apps Hungarian, the variable name guards against using it in an improper operation with the same data type by making the error obvious as in:

heightWindow = window.getWidth()

  • When programming in a language that uses dynamic typing or that is completely untyped, the decorations that refer to types cease to be redundant. Such languages typically do not include declarations of types (or make them optional), so the only sources of what types are allowed are the names themselves, documentation such as comments, and by reading the code to understand what it does. In these languages, including an indication of the type of a variable may aid the programmer. As mentioned above, Hungarian Notation expanded in such a language (BCPL).
  • In complex programs with lots of global objects (VB/Delphi Forms), having a basic prefix notation can ease the work of finding the component inside of the editor. Pressing btn<Ctrl-Space> causes the editor to pop up a list of Button objects.

Disadvantages of Systems Hungarian

Critics argue that:

  • The Hungarian notation is redundant with the type checking made by the compiler. A language providing type checking will be much more powerful to ensure that the usage of a variable is consistent with its type than the human eye would be to merely check that usage is coherent with the name of the variable.
  • Some modern Integrated development environments, such as Visual Studio display variable types on demand, and automatically flag operations which use incompatible types, making the notation largely obsolete.
  • Hungarian Notation becomes confusing when it is used to represent several properties, as in a_crszkvc30LastNameCol: a constant reference argument, holding the contents of a database column LastName of type varchar(30) which is part of the table's primary key.
  • It may lead to inconsistency when code is modified. If a variable's type is changed, either the decoration on the name of the variable will be inconsistent with the new type, or the variable's name must be changed.
  • It is inconsistent with code portability since the variable name is tied to the type. A particularly well known example is the standard WPARAM type, and the accompanying wParam formal parameter in many Windows system function declarations. It was originally a 16 bit type, but was changed to a 32 bit or 64 bit type in later versions of the operating system while retaining its original name (its true underlying type is UINT_PTR, that is, an unsigned integer large enough to hold a pointer).
  • Most of the time, knowing the use of a variable implies knowing its type. Furthermore, if you don't know what a variable is used for, knowing its type won't help you.

Notable opinions

  • Linus Torvalds (against systems Hungarian): Encoding the type of a function into the name (so-called Hungarian notation) is brain damaged - the compiler knows the types anyway and can check those, and it only confuses the programmer.
  • Steve McConnell (for Hungarian): Although the Hungarian naming convention is no longer in widespread use, the basic idea of standardizing on terse, precise abbreviations continues to have value. ... Standardized prefixes allow you to check types accurately when you're using abstract data types that your compiler can't necessarily check.
  • Bjarne Stroustrup (against systems Hungarian): No I don't recommend "Hungarian". I regard "Hungarian" (embedding an abbreviated version of a type in a variable name) a technique that can be useful in untyped languages, but is completely unsuitable for a language that supports generic programming and object-oriented programming - both of which emphasize selection of operations based on the type an arguments (known to the language or to the run-time support). In this case, "building the type of an object into names" simply complicates and minimizes abstraction.
  • Joel Spolsky (for apps Hungarian): If you read Simonyi’s paper closely, what he was getting at was the same kind of naming convention as I used in my example above where we decided that us meant “unsafe string” and s meant “safe string.” They’re both of type string. The compiler won’t help you if you assign one to the other and Intellisense won’t tell you bupkis. But they are semantically different; they need to be interpreted differently and treated differently and some kind of conversion function will need to be called if you assign one to the other or you will have a runtime bug. If you’re lucky. (...) There’s still a tremendous amount of value to Apps Hungarian, in that it increases collocation in code, which makes the code easier to read, write, debug, and maintain, and, most importantly, it makes wrong code look wrong.

Notes and references

External links

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