Echelon LonTal Stack - Manual (Page 110)

98 Using the LonTalk Interface Developer Utility
Enumerations
The LonTalk Interface Developer utility does not produce enumerations. The
LonTalk Stack requires an enumeration to be of size byte. The ANSI C standard
requires that an enumeration be an int, which is larger than one byte for many
platforms.
The LonTalk Stack enumeration uses the LON_ENUM_BEGIN and
LON_ENUM_END macros. For many compilers, these macros can be defined to
generate native enumerations:
#define LON_ENUM_BEGIN(name) enum
#define LON_ENUM_END(name)
name
Some compilers support a colon notation to define the enumeration’s underlying
type:
#define LON_ENUM_BEGIN(name) enum : signed char
#define LON_ENUM_END(name)
When your program refers to an enumerated type in a structure or union, it
should not use the enumeration’s name, but should use the LON_ENUM_*
macros.
For those compilers that support byte-sized enumerations, it can be defined as:
#define LON_ENUM(name) name
For other compilers, it can be defined as:
#define LON_ENUM(name) signed char
The following table shows an example enumeration using the LonTalk Stack
LON_ENUM_* macros, and the equivalent ANSI C enumeration.
LonTalk Stack Enumeration Equivalent ANSI C Enumeration
LON_ENUM_BEGIN(Color) {
red, green, blue
} LON_ENUM_END(Color);
typedef struct {
…
LON_ENUM(Color) color;
} Example;
enum {
red, green, blue
} Color;
typedef struct {
…
Color color;
} Example;
Floating Point Variables
Floating point variables receive special processing, because the Neuron C
compiler does not have built-in support for floating point types. Instead, it offers
an implementation for floating point arithmetic using a set of floating-point
support functions operating on a float_type type. The LonTalk Interface
Developer utility represents this type as a float_type structure, just like any
other structured type.
This floating-point format can represent numbers with the following
characteristics:
• 1038 10 * 1 ±
approximate maximum value