S-Lang function to see if a structure or field in a structure is defined
Integer_Type is_struct_defined( String_Type sf )
Determine if sf is "defined" as a field variable within a structure.
The input argument should be the name of a structure or the
name of the structure and field. The return value is 1 if the input
structure or field exists, 0 otherwise.
Note that this routine does not check whether the variable
contains any data; for this you would use the __is_initialized()
routine from the S-Lang Run-Time Library.
The variable containing the structure must be visible from other
compilation units; ie it must not be declared as either
static or private.
With the following definition:
chips> variable s = struct { foo, bar }
then we find
chips> is_struct_defined( "s" )
1
chips> is_struct_defined( "s.foo" )
1
chips> is_struct_defined( "s.bar" )
1
but
chips> is_struct_defined( "s.baz" )
0
If we repeat the previous example, but let ChIPS automatically
create the S-Lang variable for us, then we find that
the routine will always return 0. This is because the
variable is defined to have static linkage; see
"ahelp _auto_declare" for more information.
chips> r = struct { baz }
chips> is_struct_defined( "r" )
0
chips> is_struct_defined( "r.baz" )
0
Here we show the routine being used in S-Lang code run by
slsh. If the file struct.sl contains:
require("varmm");
variable a = struct { one, two };
private variable b = struct { one, two };
vmessage( "Is a.one defined? %d", is_struct_defined("a.one") );
vmessage( "Is b.two defined? %d", is_struct_defined("b.two") );
then running the code with slsh would produce
unix% slsh struct.sl
Is a.one defined? 1
Is b.two defined? 0
since the variable b was declared as being a
private variable.
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