Echelon Neuron C - Manual (Page 84)

72 How Devices Communicate Using Network Variables
Validating a Type Change
There are several ways that your application can determine if it supports a
particular SCPTnvType value. It can look for specific types, as specified by the
type_program_ID, type_scope, and type_index fields. Alternatively, it can look
for specific type categories, as defined by the type_category and type_length
fields.
The type_program_ID and type_scope values specify a program ID template and
a resource scope that together uniquely identify a resource file set. The
type_index value identifies the network variable type within that resource file
set. If the type_scope value is 0, the type_index value is a SNVT index. The
type_program_ID, type_scope, and type_index values uniquely identify a type to
your application as well as to any network tools that need to determine the
current type, or modify the type, of the network variable to which the property
applies. Your application can ignore these values if the remaining fields in the
SCPTnvType structure provide sufficient information for the application.
The type_category enumeration is defined in the <snvt_nvt.h> include file as
follows:
typedef enum nv_type_category_t {
/* 0 */ NVT_CAT_INITIAL = 0, // Initial (default)
type
/* 1 */ NVT_CAT_SIGNED_CHAR, // Signed Char
/* 2 */ NVT_CAT_UNSIGNED_CHAR, // Unsigned Char
/* 3 */ NVT_CAT_SIGNED_SHORT, // 8-bit Signed Short
/* 4 */ NVT_CAT_UNSIGNED_SHORT, // 8-bit Unsigned Short
/* 5 */ NVT_CAT_SIGNED_LONG, // 16-bit Signed Long
/* 6 */ NVT_CAT_UNSIGNED_LONG, // 16-bit Unsigned Long
/* 7 */ NVT_CAT_ENUM, // Enumeration
/* 8 */ NVT_CAT_ARRAY, // Array
/* 9 */ NVT_CAT_STRUCT, // Structure
/* 10 */ NVT_CAT_UNION, // Union
/* 11 */ NVT_CAT_BITFIELD, // Bitfield
/* 12 */ NVT_CAT_FLOAT, // 32-bit Floating Point
/* 13 */ NVT_CAT_SIGNED_QUAD, // 32-bit Signed Quad
/* 14 */ NVT_CAT_REFERENCE, // Reference
/* -1 */ NVT_CAT_NUL = -1 // Invalid Value
} nv_type_category_t;
This enumeration describes the type, stating whether it is a signed short, or
floating-point, or structure, for example, but not providing information about
structure or union fields or other similar details. The type_length field is
necessary to provide the number of bytes of a structure or union type, though it is
set for all types. To support all scalar types, test for a type_category value
between NVT_CAT_SIGNED_CHAR and NVT_UNSIGNED_LONG, plus
NVT_CAT_SIGNED_QUAD. To also support floating point types, also test for a
type_category value of NVT_FLOAT.
The SCPTnvType configuration property can be shared between multiple
changeable-type network variables. In this case, the application must make sure
to process all network variables from the property’s application set —
SCTPnvType applies to all these network variables, and so does the type change
request. The type change can only be accepted if all related network variables can
perform the required change.