Custom functions

Making C functions callable from BASIC expressions. More...

Collaboration diagram for Custom functions:

Functions
int	g2basic_register_function (const char *name, int arg_count, double(*func_ptr)(double[], int))
	Make a C function callable from BASIC expressions.

Detailed Description

Making C functions callable from BASIC expressions.

Function Documentation

g2basic_register_function()

int g2basic_register_function	(	const char *	name,
		int	arg_count,
		double(*)(double[], int)	func_ptr
	)

Make a C function callable from BASIC expressions.

BASIC code calls it as name(arg, ...). The interpreter checks the argument count before calling. It passes at most 8 arguments; more is the error too many function arguments. There is no error channel for the result: a NaN result is an ordinary value. Assigning NaN to a variable makes that variable read as undefined.

Parameters

name	Name used in BASIC; the string is copied. Names are case-sensitive, and the built-in functions are lowercase (sqrt). The name must be a valid identifier (a letter or underscore, then letters, digits, or underscores) to be callable; this is not validated. Must not be NULL.
arg_count	Required number of arguments from 0 to 8, or -1 to accept any number up to 8. A call with a different count fails with the error "function 'name' expects N arguments, got M".
func_ptr	Implementation. It receives the evaluated arguments and their count and returns the result. Must not be NULL; this is not checked.

Return values

0	The function is registered.
-1	The name is already registered (built-in functions included), or memory allocation failed. An existing function is never replaced.

static double square(double args[], int count) {
    (void)count;  // Checked by the interpreter: always 1.
    return args[0] * args[0];
}
 
g2basic_register_function("square", 1, square);
// BASIC: PRINT square(5)  ->  25