Warning: It is easy to accidentally specify arg when you meant @arg, both of which are syntactically correct (assuming arg is the name of an argument in the current context) but have vastly different meaning. To help avoid this mistake, the compiler (as of edit 1065) will treat arg as an error if it matches a current argument name; if you really meant to reference the argument by number, use a literal number or a variable that isn't a current argument.
Parameters
Note that these parameters apply to all of the .ARG... functions.
argno (Unsigned int) [in]
The ordinal number of the argument being queried, starting from 1. Note that in the case of Named Parameters, the parameter numbers are determined by the function declaration or subroutine DEFXCALL directive, not necessarily by the order specified in the calling statement. If the argno passed is invalid, the return value of the function will be -1.
@arg (Literal parameter name) [in]
This syntax provides an alternate way to reference the parameter of interest by its name rather than its ordinal number. The concept is similar to that used for XPUTARG @arg : @arg is treated by the compiler as a macro for the argument number corresponding to the argument arg as defined in the function/procedure definition or as retrieved in an SBX using XGETARG(S).
