Merge pull request #213 from adam-dziedzic/ctype_cpp_example

add C++ examples for ctypes

Author: dbader

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 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}")

python-bindings/tasks.py

@@ -64,18 +64,29 @@ def build_cmult(c, path=None):
 
 
 @invoke.task()
-def test_ctypes(c):
+def test_ctypes():
     """Run the script to test ctypes"""
-    print_banner("Testing ctypes Module")
+    print_banner("Testing ctypes Module for C")
     # pty and python3 didn't work for me (win).
     if on_win:
-        invoke.run("python ctypes_test.py")
+        invoke.run("python ctypes_c_test.py")
     else:
-        invoke.run("python3 ctypes_test.py", pty=True)
+        invoke.run("python3 ctypes_c_test.py", pty=True)
 
 
 @invoke.task()
-def build_cffi(c):
+def test_ctypes_cpp():
+    """Run the script to test ctypes"""
+    print_banner("Testing ctypes Module for C++")
+    # pty and python3 didn't work for me (win).
+    if on_win:
+        invoke.run("python ctypes_cpp_test.py")
+    else:
+        invoke.run("python3 ctypes_cpp_test.py", pty=True)
+
+
+@invoke.task()
+def build_cffi():
     """Build the CFFI Python bindings"""
     print_banner("Building CFFI Module")
     ffi = cffi.FFI()
@@ -108,14 +119,14 @@ def build_cffi(c):
 
 
 @invoke.task()
-def test_cffi(c):
+def test_cffi():
     """Run the script to test CFFI"""
     print_banner("Testing CFFI Module")
     invoke.run("python cffi_test.py", pty=not on_win)
 
 
 @invoke.task()
-def build_cppmult(c):
+def build_cppmult():
     """Build the shared library for the sample C++ code"""
     print_banner("Building C++ Library")
     invoke.run(
@@ -137,22 +148,22 @@ def compile_python_module(cpp_name, extension_name):
 
 
 @invoke.task(build_cppmult)
-def build_pybind11(c):
+def build_pybind11():
     """Build the pybind11 wrapper library"""
     print_banner("Building PyBind11 Module")
     compile_python_module("pybind11_wrapper.cpp", "pybind11_example")
     print("* Complete")
 
 
 @invoke.task()
-def test_pybind11(c):
+def test_pybind11():
     """Run the script to test PyBind11"""
     print_banner("Testing PyBind11 Module")
     invoke.run("python3 pybind11_test.py", pty=True)
 
 
 @invoke.task(build_cppmult)
-def build_cython(c):
+def build_cython():
     """Build the cython extension module"""
     print_banner("Building Cython Module")
     # Run cython on the pyx file to create a .cpp file
@@ -164,7 +175,7 @@ def build_cython(c):
 
 
 @invoke.task()
-def test_cython(c):
+def test_cython():
     """Run the script to test Cython"""
     print_banner("Testing Cython Module")
     invoke.run("python3 cython_test.py", pty=True)
@@ -173,7 +184,9 @@ def test_cython(c):
 @invoke.task(
     clean,
     build_cmult,
+    build_cppmult,
     test_ctypes,
+    test_ctypes_cpp,
     build_cffi,
     test_cffi,
     build_pybind11,