Struct Dereference Operator (->)
Access the members of a Struct by name.
StructVariable->MemberName | StructFunction
Arguments
- StructVariable—variable or parameter of type struct which refers to one or more Structs
- MemberName—Struct member identifier; can be a literal name or a
string; for example
mem
or"mem"
. An empty string""
returns Structs with no name. - Function—Struct function. For more information, see ProcScript: Struct Functions.
Return Values
Returns an ordered collection of references to members of the Struct to which StructVariable refers.
If StructVariable refers to a collection of Structs rather than to a single Struct, the expression is evaluated for each Struct in the collection, and the resulting collections are combined into a single ordered collection of Structs.
If there are no members that satisfy the criteria, the result is NULL and an error is set in $procerror.
Error number | Error Constant | Meaning |
---|---|---|
-84
|
ACTERR_NO_OBJECT
|
Struct operator applied to non-Struct |
-1153
|
USTRUCTERR_INDEX_NOT_ALLOWED
|
Struct index is not allowed |
-1155
|
USTRUCTERR_MEMBER_NOT_FOUND . |
The Struct does not contain a member with the specified name. |
-1157
|
USTRUCTERR_ILLEGAL_MEMBER_TYPE
|
StructVariable is not of type struct or any |
Use
Allowed in all components.
Description
The arrow -> is known as the dereference operator because the Struct being referred to changes (is de-referenced) from the one on the left to the one on the right. The dereference operator can be used multiple times in a statement to travers the nested levels of a Struct to get to the Struct member you need. For example, if you have a Struct referring to book that includes a Preface, you need to start from the top of the Struct nad use the dereference operator to get the Preface, and use it again to get the Acknowledgements section:
vStruct = Book->Preface->Acknowledgements
You can use the dereference operator to address Structs by name. By specifying an empty
string (""
), you can access nameless Structs. By using the *
asterisk wildcard after the operator, you can get a collection of references to all members of a
Struct.
Important: The * wildcard can only be used after the dereference operator. It cannot
be used in constructs such as vStruct->c*
to get all Structs whose names begin
with c
. ->* is actually a separate operator (the Struct collection
operator).
Member Names as Strings
MemberName can be specified as a string, which means that it is possible to:
- Use string substitution to access a field name. For example, the following code
returns the members with the name as specified in field F1.
vStruct->"%%F1%%%"
- Specify member names that include any character, including spaces,
#
, and$
.vStruct->"first name"
- Address Struct members that have an empty string as name:
vStruct->""
If a Struct has several members with the same name, you can access one of these members specifically, by using the dereference operator in combination with the struct index operator {N}. For example:
vBookStruct->chapter{2}