If you are on Linux, there is a handy utility nm to list the content of a shared library (there is always a handy utility on Linux, especially for C stuff).

Here is the question about it.

You use it with the -D flag: nm -D ./libMyLib.so

How do I code a C function to accept a list as its arguments?

Short answer, you can't.

Long answer: C does not have lists, but has arrays and pointers.

You have several options then:

int c_func(const char *dir, float abcd[4]) { // using an array with explicit size

int c_func(const char *dir, float abcd[]) { // Using an array (will decay to a pointer at compile-time)

int c_func(const char *dir, float *abcd) { // Using a pointer.

If you will only ever receive 4 floats, I'd suggest the first form, which enforces the size of the array, any user (and mainly your future self) of your function will know to give only an array of four elements.

Calling your function from Python:

floats = [1.0, 2.0, 3.0, 4.0] # Or whatever values you want to pass, but be sure to give only 4
FloatArray4 = ctypes.c_float * 4 # Define a 4-length array of floats
parameter_array = FloatArray4(*floats) # Define the actual array to pass to your C function

I don't know if passing more than 4 floats to FloatArray4 raises an error -- I guess so, but I can't check right now.

As for your second question, if you want dynamic sized arrays (more than 4 elements), you'll have to you one of the other two profiles for your C function, in which case I advise you to put an extra int argument for the size of the array:

int c_func(const char *dir, float floats[], int size) {

or

int c_func(const char *dir, float *floats, int size) {

You can also use the standard size_t instead of int, it's designed just for that.

I you want to pass a multidimensional array, you add another pair of brackets:

int c_func(const char *dir, float floats[][4]) { // Note the explicit size for second dimension

but remember that for a C array, for all dimensions but the first, the dimensions must be explicitly specified. If the value is constant it wont be an issue, however if not you will have to use a pointer instead:

int c_func(const char *dir, float *floats[]) {

or

int c_func(const char *dir, float **floats) {

which are two identical syntaxs (the array will decay to a pointer). Once again, if your dimensions are dynamic, I suggest to add parameters for the size.

If you want supplementary dimensions, just repeat that last step.

The following code works on arbitrary lists:

import ctypes
py_values = [1, 2, 3, 4]
arr = (ctypes.c_int * len(py_values))(*py_values)