add C++ examples for ctypes

Author: adam-dziedzic

python-bindings/cppmult.hpp

@@ -1 +1,15 @@
-float cppmult(int int_param, float float_param);
+#ifdef _MSC_VER
+    #define EXPORT_SYMBOL __declspec(dllexport)
+#else
+    #define EXPORT_SYMBOL
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+EXPORT_SYMBOL float cppmult(int int_param, float float_param);
+
+#ifdef __cplusplus
+}
+#endif

python-bindings/ctypes_test.py python-bindings/ctypes_c_test.pypython-bindings/ctypes_test.py renamed to python-bindings/ctypes_c_test.py

@@ -2,13 +2,17 @@
 """ Simple examples of calling C functions through ctypes module. """
 import ctypes
 import sys
+import pathlib
 
 if __name__ == "__main__":
+    libname = pathlib.Path().absolute()
+    print('libname: ', libname)
+
     # Load the shared library into c types.
     if sys.platform.startswith("win"):
-        c_lib = ctypes.CDLL("cmult.dll")
+        c_lib = ctypes.CDLL(libname / "cmult.dll")
     else:
-        c_lib = ctypes.CDLL("libcmult.so")
+        c_lib = ctypes.CDLL(libname / "libcmult.so")
 
     # Sample data for our call:
     x, y = 6, 2.3

python-bindings/ctypes_cpp_test.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python
+""" Simple examples of calling C functions through ctypes module. """
+import ctypes
+import sys
+import pathlib
+
+if __name__ == "__main__":
+    libname = pathlib.Path().absolute()
+    print('libname: ', libname)
+
+    # Load the shared library into c types.
+    if sys.platform.startswith("win"):
+        c_lib = ctypes.CDLL(libname / "cppmult.dll")
+    else:
+        c_lib = ctypes.CDLL(libname / "libcppmult.so")
+
+    # Sample data for our call:
+    x, y = 6, 2.3
+
+    # This will not work:
+    # answer = c_lib.cmult(x, y)
+
+    # This produces a bad answer:
+    answer = c_lib.cppmult(x, ctypes.c_float(y))
+    print(f"    In Python: int: {x} float {y:.1f} return val {answer:.1f}")
+    print()
+
+    # You need tell ctypes that the function returns a float
+    c_lib.cppmult.restype = ctypes.c_float
+    answer = c_lib.cppmult(x, ctypes.c_float(y))
+    print(f"    In Python: int: {x} float {y:.1f} return val {answer:.1f}")