Hungarian notation

The mnemonics for pointers and

• pszOwner : pointer to zero-terminated string
• rgfpBalances : array of
  floating-point
  values
• aulColors : array of unsigned long (Systems)

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. In particular, use of Hungarian notation was widely evangelized by Charles Petzold's "Programming Windows", the original (and for many readers, the definitive) book on Windows API programming. Thus, many commonly seen constructs of Hungarian notation are specific to Windows:

• For programmers who learned Windows programming in C, probably the most memorable examples are the wParam (word-size parameter) and lParam (long-integer parameter) for the WindowProc() function.
• hwndFoo : handle to a window
• lpszBar : long pointer to a zero-terminated string

The notation is sometimes extended in

In JavaScript code using jQuery, a $ prefix is often used to indicate that a variable holds a jQuery object (versus a plain DOM object or some other value).^[7]

Advantages

(Some of these apply to Systems Hungarian only.)

Supporters argue that the benefits of Hungarian Notation include:^[3]

• The symbol type can be seen from its name. This is useful when looking at the code outside an integrated development environment — like on a code review or printout — or when the symbol declaration is in another file from the point of use, such as a function.
• In a language that uses
  dynamic typing or that is untyped, the decorations that refer to types cease to be redundant. In such languages variables are typically not declared as holding a particular type of data, so the only clue as to what operations can be done on it are hints given by the programmer, such as a variable naming scheme, documentation and comments. As mentioned above, Hungarian Notation expanded in such a language (BCPL
  ).
• The formatting of variable names may simplify some aspects of code refactoring (while making other aspects more error-prone).
• 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.
• Inappropriate type casting and operations using incompatible types can be detected easily while reading code.
• In complex programs with many global objects (VB/Delphi Forms), having a basic prefix notation can ease the work of finding the component inside of the editor. For example, searching for the string btn might find all the Button objects.
• Applying Hungarian notation in a narrower way, such as applying only for member variables, helps avoid naming collision.
• Printed code is more clear to the reader in case of datatypes, type conversions, assignments, truncations, etc.

Disadvantages

Most arguments against Hungarian notation are against Systems Hungarian notation, not Apps Hungarian notation. Some potential issues are:

• The Hungarian notation is redundant when type-checking is done by the compiler. Compilers for languages providing strict type-checking, such as Pascal, ensure the usage of a variable is consistent with its type automatically; checks by eye are redundant and subject to human error.
• Most modern integrated development environments 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
  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 or ported. 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. A particularly well known example is the standard WPARAM type, and the accompanying wParam
  formal parameter
  in many Windows system function declarations. The 'w' stands for 'word', where 'word' is the native word size of the platform's hardware architecture. It was originally a 16 bit type on 16-bit word architectures, but was changed to a 32-bit on 32-bit word architectures, or 64-bit type on 64-bit word architectures 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). The semantic impedance, and hence programmer confusion and inconsistency from platform-to-platform, is on the assumption that 'w' stands for a two byte, 16-bit word in those different environments.
• Most of the time, knowing the use of a variable implies knowing its type. Furthermore, if the usage of a variable is not known, it cannot be deduced from its type.
• Hungarian notation reduces the benefits of using code editors that support completion on variable names, for the programmer has to input the type specifier first, which is more likely to collide with other variables than when using other naming schemes.
• It makes code less readable, by obfuscating the purpose of the variable with type and scoping prefixes.[8]
• The additional type information can insufficiently replace more descriptive names. E.g. sDatabase does not tell the reader what it is. databaseName might be a more descriptive name.
• When names are sufficiently descriptive, the additional type information can be redundant. E.g. firstName is most likely a string. So naming it sFirstName only adds clutter to the code.
• It's harder to remember the names.
• Multiple variables with different semantics can be used in a block of code with similar names: dwTmp, iTmp, fTmp, dTmp.
• Placing data type or intent character identifiers as a prefix to the field or variable's Given name subverts the ability, in some programming environments, to jump to a field or variable name, alphabetically, when the user begins typing the name. FileMaker, ^[9] for example, is one such programming environment. It may be preferable when using one of these programming environments to instead suffix Given names with such identifying characters.

Notable opinions

• Robert Cecil Martin (against Hungarian notation and all other forms of encoding):

  ... nowadays HN and other forms of type encoding are simply impediments. They make it harder to change the name or type of a variable, function, member or class. They make it harder to read the code. And they create the possibility that the encoding system will mislead the reader.^[10]

• 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.^[11]

• Steve McConnell (for Apps 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.^[12]

• Bjarne Stroustrup (against Systems Hungarian for C++):

  No I don't recommend 'Hungarian'. I regard 'Hungarian' (embedding an abbreviated version of a type in a variable name) as 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 and 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.^[13]

• intelligent code completion system] 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.... (Systems Hungarian) was a subtle but complete misunderstanding of Simonyi’s intention and practice.^[4]

• Microsoft's Design Guidelines^[14] discourage developers from using Systems Hungarian notation when they choose names for the elements in .NET class libraries, although it was common on prior Microsoft development platforms like Visual Basic 6 and earlier. These Design Guidelines are silent on the naming conventions for local variables inside functions.

See also

• Leszynski naming convention, a variant of Hungarian for database development
• Camel case, another widespread naming convention
• Polish notation, an unrelated concept with a similar name

References