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C Style: Standards and Guidelines (contents)

CHAPTER 5 : Naming

PART 2 : COMMENTING AND NAMING

CHAPTER 5 : Naming
5.1 Constraints upon naming
5.2 Abbreviations
5.3 Short names
5.4 Separating words
5.5 Spelling of names
5.6 Naming functions
5.7 Indicating functional group
5.8 Naming variables
5.9 Indicating type
5.10 Naming replacement items
5.11 Naming Files and Directories
5.12 Summary

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5.9  Indicating type

Some advantage may be gained from indicating the type of the variable in its name. A common example is the suffix 'ptr' used to indicate a pointer:

 

ParaPtr, FirstFreeBlockPtr

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An alternative approach (sometimes known as the 'Hungarian' method), which can be used to indicate any type, is to prefix the name with a lower case letter:

 

pPara, pFirstFreeBlock

 

This reads naturally: "pointer to a paragraph", "Pointer to the first free block". It also helps to know immediately that the variable is a pointer, putting it directly into context.

Even more so than functional prefixes, a type indicator needs to be differentiated from the name. The lowercase letter works well with a following capital. An alternative, which would work with a lowercase naming scheme, is to separate the type identifier with an underscore, possibly also making it a suffix:

 

para_p, first_free_block_p

 

The type of any item can be indicated in a similar manner. The only important rules are (a) to be consistent and (b) to make sure that the set of prefixes and their use are clearly documented. Candidates include:

 

Prefix           Meaning

  b             Boolean

  c             Character

  i             Integer

  l             Long

  u                Unsigned

  p             Pointer

  a             Array

  f             Bit flags

  h             File Handle

  z             Zero terminated character array

  s             structure

 

Note that using the 'b' prefix for boolean can be an alternative to using 'Is' as above (see 5.8.2), thus:

 

bDoorOpen    ...or...    DoorIsOpen

 

Type prefixes can show up some potential problems in the code, and undesirable or illegal operations become immediately visible.

 

aEmpNames[0] = '\0';     /* this is ok          */    
*aEmpNames = '\0';       /* this is undesirable */
aEmpNames++;             /* this is illegal     */

 

Types can be combined, thus 'int *apWidgetSizes[]' is an array of pointers to integers. Thus rather than having to work out what 'WidgetSizes' is from the context, it is clear from the name.

The type of return from a function can similarly be shown with a prefix. Thus a function returning a pointer to a structure might be 'psGetWindow()'.

 

This prefixing method can be confusing, especially where there are many prefixes to learn, where they are used in combination with a functional prefix, or with an all-lower case naming standard. Also, where the variable has a relatively short scope, the use of such prefixing has less value.

A compromise is to define a limited set for types which are most likely to cause confusion and error. e.g:

 

Prefix           Meaning

  p             pointer

  a             array

  h             handle

  u             unsigned

 

This book uses only 'p' as a prefix for pointers.

 

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