From 6c0848ab01960292987b4876c7b3bb3391903e07 Mon Sep 17 00:00:00 2001
From: Wolfgang Hottgenroth <wolfgang.hottgenroth@icloud.com>
Date: Sat, 12 Dec 2020 20:24:58 +0100
Subject: [PATCH] offsetof related experiments

---
 offsetTest/Makefile | 17 ++++++++++++++++
 offsetTest/test.c   | 47 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)
 create mode 100644 offsetTest/Makefile
 create mode 100644 offsetTest/test.c

diff --git a/offsetTest/Makefile b/offsetTest/Makefile
new file mode 100644
index 0000000..c1a51ca
--- /dev/null
+++ b/offsetTest/Makefile
@@ -0,0 +1,17 @@
+CFLAGS=
+
+test:	test.o
+	gcc -o $@  $^
+
+test.o:	test.c
+	gcc -c -o $@ $(CFLAGS) $^
+
+
+.PHONY: run
+run:	test
+	./test
+
+.PHONY: clean
+clean:
+	rm -f *.o test
+
diff --git a/offsetTest/test.c b/offsetTest/test.c
new file mode 100644
index 0000000..4e6ce27
--- /dev/null
+++ b/offsetTest/test.c
@@ -0,0 +1,47 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <stddef.h>
+
+typedef struct {
+  uint8_t id;
+  char a[16];
+  uint8_t length;
+} t_testObj;
+  
+t_testObj testObj = { .id = 0, .a = "test123", .length = 25 };
+
+void printTestObj(t_testObj *testObj) {
+  printf("testObj: id=%d, a=%s, length=%d\n", testObj->id, testObj->a, testObj->length);
+}
+
+int main() {
+  printf("id:     %ld\n", offsetof(t_testObj, id));
+  printf("a:      %ld\n", offsetof(t_testObj, a));
+  printf("length: %ld\n", offsetof(t_testObj, length));
+
+  printTestObj(&testObj);
+
+  strcpy(testObj.a, "demo234");
+  printTestObj(&testObj);
+
+  uint8_t *a1 = (uint8_t*)&testObj;
+  printf("a1: %p\n", a1);
+
+  uint8_t *a2 = ((uint8_t*)&testObj) + offsetof(t_testObj, length);
+  printf("a2: %p\n", a2);
+
+  *a2 = 35;
+  printTestObj(&testObj);
+
+  uint8_t *a3 = ((uint8_t*)&testObj) + offsetof(t_testObj, a);
+  printf("a3: %p\n", a3);
+
+  strcpy((char*)a3, "Wolfgang");
+  printTestObj(&testObj);
+}
+
+
+
+