When the object's memory layout is decided it can't be adjusted

Author: Wang Jiazi

C++/MemoryModel/packed.cpp

@@ -0,0 +1,49 @@
+#include <stdio.h>
+struct People 
+{
+    int age;
+    char c;
+}__attribute__((packed));
+
+
+struct People_unpack
+{
+    int age;
+    char c;
+};
+
+
+//5 Bytes
+struct Student1
+{
+    People p;
+};
+
+//16 Bytes
+struct Student2
+{
+    People p;
+    double scores;
+};
+
+//13 Bytes
+struct Student3
+{
+    People p;
+    double scores;
+}__attribute__((packed));
+
+//16 Bytes
+struct Student4
+{
+    People_unpack p;
+    double scores;
+}__attribute__((packed));
+
+int main()
+{
+    struct People P;
+    struct People_unpack P2;
+    printf("%d %d sizeof(Student1)=%d, sizeof(Student2)=%d, sizeof(Student3)=%d, sizeof(Student4)=%d\n",sizeof(P), sizeof(P2),
+                                sizeof(Student1), sizeof(Student2), sizeof(Student3), sizeof(Student4));
+}