PROTO Procedure

Interfacing with External C Functions

To make it easier to interface with external C functions, many PROTO-compatible procedures have been enhanced to support most of these C types.

There is no way to return and save a pointer to any type in a SAS variable (see Automatic Type Casting for the short Data Type in an Assignment Statement.) Pointers are always dereferenced, and their contents are converted and copied to SAS variables.

The EXTERNC statement is used to specify C variables in PROTO compatible procedures. The syntax of the EXTERNC statement has the following form:

EXTERNC DOUBLE | INT | LONG | SHORT | CHAR <[*][*]> var-1 <var-2 ... var-n>;

The following table shows how these variables are treated when they are positioned on the left side of an expression. The table shows the automatic casting that is performed for a short type on the right side of an assignment. (Explicit type conversions can be forced in any expression, with a unary operator called a cast.) The table lists all the allowed combinations of short types that are associated with SAS variables.

Note: A table for int, long, and double types can be created by substituting any of these types for “short” in this table.

If any of the pointers are null and require dereferencing, then the result is set to missing if there is a missing value set for the result variable. For more information, see MAPMISS Statement.

Automatic Type Casting for the short Data Type in an Assignment Statement

Type for Left Side of Assignment	Type for Right Side of Assignment	Cast Performed
short	SAS numeric	y = (short) x
short	short	y = x
short	short *	y = * x
short	short **	y = ** x
short *	SAS numeric	* y = (short) x
short *	short	y = & x
short *	short *	y = x
short *	short **	y = * x
short **	SAS numeric	**y = (short) x
short **	short *	y = & x
short **	short **	y = x
SAS numeric	short	y = (double) x
SAS numeric	short *	y = (double) * x
SAS numeric	short **	y = (double) ** x

The following table shows how these variables are treated when they are passed as arguments to an external C function.

Types That Are Allowed for External C Arguments

Function Prototype	SAS Variable Type	C Variable Type
short	numeric	short, short , short *
short *	numeric, array	short, short , short *
short **	array	short , short *
int	numeric	int, int , int *
int *	numeric, array	int, int , int *
int **	array	int , int *
long	numeric	long, long , long *
long *	numeric, array	long, long , long *
long **	array	long , long *
double	numeric	double, double , double *
double *	numeric, array	double, double , double *
double **	array	double , double *
char *	character	char , char *
char **	character	char , char *
struct *	structure	struct , struct *
struct **	structure	struct , struct *

Note: Automatic conversion between two different C types is never performed.