adds container_of

CMakeLists.txt

@@ -272,6 +272,7 @@ pkg_check_modules(GMOCK gmock)
 add_executable(alltests
 	test/msleep.cc
 	test/mock_authenticator.cc
+	test/test_container_of.cc
 	test/test_response_parser.cc
 	test/test_server.cc
 	test/test_timepoint.cc

lib/webfuse/core/container_of.h

@@ -0,0 +1,16 @@
+#ifndef WF_CONTAINER_OF_H
+#define WF_CONTAINER_OF_H
+
+#ifndef __cplusplus
+#include <stddef.h>
+#else
+#include <cstddef>
+#endif
+
+#define WF_CONTAINER_OF(pointer, type, member) \
+    ({ \
+        const typeof( ((type *)0)->member ) *__mptr = (pointer); \
+        (type *)( (char *)__mptr - offsetof(type, member) ); \
+    })
+
+#endif

test/test_container_of.cc

@@ -0,0 +1,29 @@
+#include <gtest/gtest.h>
+#include "webfuse/core/container_of.h"
+
+namespace
+{
+
+struct MyStruct
+{
+    int first;
+    int second;
+};
+
+}
+
+TEST(ContainerOf, FirstMember)
+{
+    MyStruct my_struct = {23, 42};
+
+    int * first = &my_struct.first;
+    ASSERT_EQ(&my_struct, WF_CONTAINER_OF(first, MyStruct, first));
+}
+
+TEST(ContainerOf, SecondMember)
+{
+    MyStruct my_struct = {23, 42};
+
+    int * second = &my_struct.second;
+    ASSERT_EQ(&my_struct, WF_CONTAINER_OF(second, MyStruct, second));
+}