User Manual

LonTalk Stack Developer’s Guide 121
Validating a Type Change
The SCPTnvType configuration property is defined by the following structure:
typedef LON_STRUCT_BEGIN(SCPTnvType) {
ncuInt type_program_ID[8];
ncuInt type_scope;
ncuLong type_index;
ncsInt type_category;
ncuInt type_length;
ncsLong scaling_factor_a;
ncsLong scaling_factor_b;
ncsLong scaling_factor_c;
} LON_STRUCT_END(SCPTnvType);
When validating a change to a network variable, an application can check five of
the fields in the SCPTnvType configuration property:
• The program ID template of the resource file that contains the network
variable type definition (type_program_ID[8])
• The scope of the resource file that contains the network variable type
definition (type_scope)
• The index within the specified resource file of the network variable type
definition (type_index)
• The category of the network variable type (type_category)
• The length of the network variable type (type_length)
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. For
example, checking the type_scope and type_program_ID fields lets you accept
only types that you created.
The type_category enumeration is defined in the <snvt_nvt.h> include file as:
typedef enum nv_type_category_t {
NVT_CAT_INITIAL = 0, // Initial (default) type
NVT_CAT_SIGNED_CHAR, // Signed Char
NVT_CAT_UNSIGNED_CHAR, // Unsigned Char
NVT_CAT_SIGNED_SHORT, // 8-bit Signed Short
NVT_CAT_UNSIGNED_SHORT, // 8-bit Unsigned Short
NVT_CAT_SIGNED_LONG, // 16-bit Signed Long
NVT_CAT_UNSIGNED_LONG, // 16-bit Unsigned Long
NVT_CAT_ENUM, // Enumeration
NVT_CAT_ARRAY, // Array
NVT_CAT_STRUCT, // Structure
NVT_CAT_UNION, // Union
NVT_CAT_BITFIELD, // Bitfield
NVT_CAT_FLOAT, // 32-bit Floating Point
NVT_CAT_SIGNED_QUAD, // 32-bit Signed Quad
NVT_CAT_REFERENCE, // Reference
NVT_CAT_NUL = -1 // Invalid Value
} nv_type_category_t;