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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

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