/sys$common/syshlp/helplib.hlb CC, /DEFINE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

     /DEFINE=(identifier[=definition][,...])
     /NODEFINE (D)

  Performs the same function as the #define preprocessor directive.
  That is, /DEFINE defines a token string or macro to be substituted
  for every occurrence of a given identifier in the program.

  DCL converts all input to uppercase unless it is enclosed in
  quotation marks.

  The simplest form of a /DEFINE definition is:

  /DEFINE=true

  This results in a definition like the one that would result from
  the following definition:

  #define TRUE 1

  Macro definitions must be enclosed in quotation marks as shown in
  the following definition:

  /DEFINE="funct(a)=a+sin(a)"

  This definition produces the same results as the following
  definition:

  #define funct(a) a+sin(a)

  When more than one /DEFINE is present on the CC command line or in
  a single compilation unit, only the last /DEFINE is used.

  When both /DEFINE and /UNDEFINE are present in a command line,
  /DEFINE is evaluated before /UNDEFINE.

  The default is /NODEFINE.