memory arithmetics classwork

classwork/CMakeLists.txt

@@ -2,5 +2,6 @@
 
 add_executable (classwork "main.cpp" "main.h")
 add_executable (vehicles "vehicle.cpp" "vehicle.h")
+add_executable (memarith "memarith.cpp" "memarith.h")
 
 # TODO: Add tests and install targets if needed.

classwork/main.cpp

@@ -1,25 +1,6 @@
 #include <iostream>
 using namespace std;
 
-class A {
-    string a_s;
-    friend int main();
-public:
-    string getBString() const { /* TODO: return B::b_s value */; }
-};
-class B : public A {
-    string b_s;
-    friend int main();
-public:
-    B() { b_s = "It's b!"; }
-};
-
 int main()
 {
-    B b;
-    A *a = &b;
-    cout << "b address is " << &b << ", a_s address is " << &b.a_s << ", b_s address is " << &b.b_s << endl;
-    cout << "b size is " << sizeof(b) << ", a_s size is " << sizeof(b.a_s) << endl;
-    cout << "b_s is '" << a->getBString() << "'" << endl;
-	return 0;
 }

classwork/memarith.cpp

@@ -0,0 +1,14 @@
+#include <iostream>
+#include "memarith.h"
+
+using namespace std;
+
+int main()
+{
+    B b;
+    A *a = &b;
+    cout << "b address is " << &b << ", a_s address is " << &b.a_s << ", b_s address is " << &b.b_s << endl;
+    cout << "b size is " << sizeof(b) << ", a_s size is " << sizeof(b.a_s) << endl;
+    cout << "b_s is '" << a->getBString() << "'" << endl;
+    return 0;
+}

classwork/memarith.h

@@ -0,0 +1,27 @@
+#include <string>
+
+class A {
+    std::string a_s;
+    int foo;
+
+    friend int main();  // for debugging display purposes
+
+public:
+    std::string getBString() const { return *((const std::string *)(this + 1)); }
+    float getBData(int idx) const { return ((const float *)((const std::string *)(this + 1)))[idx]; }
+};
+
+class B : public A {
+    std::string b_s;
+    float data[7];
+
+    friend int main();  // for debugging display purposes
+
+public:
+    B() { b_s = "It's b!"; }
+};
+
+// | class B
+// | class A  | self   |
+// | a_s; foo | b_s    |
+// адрес b_s = адрес b плюс смещение b_s относительно начала b = адрес b плюс размер A