167. Calling the modf() foreign function

Let’s consider that we want to call the modf() foreign function. This function is part of the C standard library with the following syntax (https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/modf-modff-modfl):

double modf(double x, double *intptr);

This method gets a double x and returns the signed fractional part of x. The intptr is a pointer argument used to point to the memory address where the integer part should be stored as a double value.

Since this method is part of UCRT, it can be found via defaultLookup():

Linker linker = Linker.nativeLinker();
SymbolLookup libLookup = linker.defaultLookup();
try (Arena arena = Arena.ofConfined()) {
  MemorySegment segmentModf = libLookup.find("modf").get();
  ...

Nothing new so far! Next, we need to define the proper MethodHandle. Because the second argument of modf() is a pointer, we need to specify a value layout of type ADDRESS:

  MethodHandle...