In this section of the tutorial, I’m going to write about the
As you can see (in the code available here), the function takes three arguments. These are generic arguments, used in the
*_new() function of every external you’ll write. The arguments are as follows:
t_symbol *s – a pointer to the symbolic representation of the objects name. You don’t have to worry about this, it’s for PD.
int argc – the number of arguments the user has entered, following the name of the object.
t_atom *argv – a pointer to the first of these arguments.
argc to tell you how many arguments to read, starting from the
argv pointer. This allows you to create an object that uses default values if a user doesn’t enter all of the required arguments.
randomwalk.c, I’m using a
switch statement to check the number of arguments provided, and then read the user-provided arguments into their proper variables. The
atom_getfloat() function simply takes one of the arguments (of the PD type
atom) and returns a C/C++ float, which can be assigned to a variable.
Below that, I reuse the
argc count to determine which variables have to be assigned to defaults. Finally, I do some error checking to make sure that the highbound is actually a higher number than the lowbound, and swap if needed. This kind of error checking is very important to avoid crashes when actually using the object.
Finally, we have to assign inlets and outlets. The three calls to
floatinlet_new() assign inlets which allow direct assignment of the lower, upper, and step variables from PD. There should probably be some error checking here too, because what would happen if a user input a list or a symbol instead? We also define
f_out to be an outlet, using
outlet_new() which takes two arguments, a reference to the object itself, and the type of value that will be output.
The return statement simply returns the initialized object to PD, ready for use.