better weak pointer explanation

Author: sjoerdev

content/posts/cpp-for-cscharp.md

@@ -178,7 +178,9 @@ What makes this one different from the other smart pointers:
 - there can be many weak pointers per object
 - weak pointers dont increase the amount of shares like a shared pointer
 - weak pointers dont own an object so the object's lifetime is not tied to the weak ptr
-- all weak pointers expire (points to nullptr) when the last shared ptr gets dropped
+- all weak pointers expire when the last shared ptr gets dropped
+- weak pointers dont point to anything directly, so you cant simply deref them
+- to use a weak pointer you must convert it to a temporary shared pointer
 
 ```cpp
 // cpp
@@ -196,6 +198,22 @@ void test()
     // get amount of shares
     int shares = sp.use_count(); // still 1, weak ptr didnt add a share
 
+    // directly dereferencing a weak pointer wont work
+    // *wp and wp-> cause a compile time error
+    // to use a weak pointer you must convert it to a temp shared pointer
+    // lock creates a shared pointer if the object still exists otherwise a nullptr
+    auto temp_sp = wp.lock()
+    if (temp_sp != nullptr)
+    {
+        // safe to use *temp_sp or temp_sp->
+        
+        // while the temporary shared pointer exists there is an extra share
+        int shares = sp.use_count(); // now 2 temporarily
+
+        // drop temp shared pointer
+        temp_sp.reset();
+    }
+
     // destroy the only and last shared pointer with ownership
     sp.reset();