Updated comments for the heap allocated (thread unsage) mpStmtRefCount ref counter shared between Statement and Column objects

src/SQLiteC++/Column.cpp

@@ -21,19 +21,19 @@ Column::Column(sqlite3* apSQLite, sqlite3_stmt* apStmt, unsigned int* apStmtRefC
     mpStmtRefCount(apStmtRefCount),
     mIndex(aIndex)
 {
+    // Increment the reference counter of the sqlite3_stmt,
+    // telling the Statement object not to finalize the sqlite3_stmt during the lifetime of this Column objet
     (*mpStmtRefCount)++;
 }
 
 // Finalize and unregister the SQL query from the SQLite Database Connection.
 Column::~Column(void) throw() // nothrow
 {
-    // Decrement and check the reference counter
+    // Decrement and check the reference counter of the sqlite3_stmt
     (*mpStmtRefCount)--;
     if (0 == *mpStmtRefCount)
     {
-        // When count reaches zero, dealloc and finalize the statement
-        delete mpStmtRefCount;
-
+        // When count reaches zero, finalize the sqlite3_stmt, as no Column nor Statement object use it any more
         int ret = sqlite3_finalize(mpStmt);
         if (SQLITE_OK != ret)
         {
@@ -41,7 +41,11 @@ Column::~Column(void) throw() // nothrow
             //std::cout << sqlite3_errmsg(mpSQLite);
         }
         mpStmt = NULL;
+
+        // and delete the reference counter
+        delete mpStmtRefCount;
     }
+    // else, the finalization will be done by the Statement or another Column object (the last one)
 }
 
 // Return the integer value of the column specified by its index starting at 0

src/SQLiteC++/Column.h

@@ -20,6 +20,8 @@ namespace SQLite
  * @brief Encapsulation of a Column in a Row of the result.
  *
  * A Column is a particular field of SQLite data in the current row of result of the Statement.
+ *
+ * @todo mpStmtRefCount is thread unsafe !
  */
 class Column
 {
@@ -84,7 +86,7 @@ private:
 private:
     sqlite3*        mpSQLite;       //!< Pointer to SQLite Database Connection Handle
     sqlite3_stmt*   mpStmt;         //!< Pointer to SQLite Statement Object
-    unsigned int*   mpStmtRefCount; //!< Pointer to the reference counter of the Statement Object (to share it with a Statement object)
+    unsigned int*   mpStmtRefCount; //!< Pointer to the heap allocated reference counter of the sqlite3_stmt (shared with the Statement object)
     int             mIndex;         //!< Index of the column in the row of result
 };
 

src/SQLiteC++/Statement.cpp

@@ -28,7 +28,8 @@ Statement::Statement(Database &aDatabase, const char* apQuery) : // throw(SQLite
     int ret = sqlite3_prepare_v2(mpSQLite, mQuery.c_str(), mQuery.size(), &mpStmt, NULL);
     check(ret);
     mColumnCount = sqlite3_column_count(mpStmt);
-    // Initialize the reference counter of the Statement Object : used to share the mpStmt with Column objects
+    // Initialize the reference counter of the sqlite3_stmt : used to share the mpStmt with Column objects;
+    // This is needed to enable Column objects to live longer than the Statement objet it refers to.
     mpStmtRefCount = new unsigned int;
     *mpStmtRefCount = 1;
 }
@@ -36,13 +37,11 @@ Statement::Statement(Database &aDatabase, const char* apQuery) : // throw(SQLite
 // Finalize and unregister the SQL query from the SQLite Database Connection.
 Statement::~Statement(void) throw() // nothrow
 {
-    // Decrement and check the reference counter
+    // Decrement and check the reference counter of the sqlite3_stmt
     (*mpStmtRefCount)--;
     if (0 == *mpStmtRefCount)
     {
-        // When count reaches zero, dealloc and finalize the statement
-        delete mpStmtRefCount;
-
+        // If count reaches zero, finalize the sqlite3_stmt, as no Column objet use it anymore
         int ret = sqlite3_finalize(mpStmt);
         if (SQLITE_OK != ret)
         {
@@ -50,7 +49,11 @@ Statement::~Statement(void) throw() // nothrow
             //std::cout << sqlite3_errmsg(mpSQLite);
         }
         mpStmt = NULL;
+
+        // and delete the reference counter
+        delete mpStmtRefCount;
     }
+    // else, the finalization will be done by the last Column object
 }
 
 // Reset the statement to make it ready for a new execution

src/SQLiteC++/Statement.h

@@ -28,6 +28,8 @@ class Column;
  * Resource Acquisition Is Initialization (RAII) means that the Statement
  * is compiled in the constructor and finalized in the destructor, so that there is
  * no need to worry about memory management or the validity of the underlying SQLite Statement.
+ *
+ * @todo mpStmtRefCount is thread unsafe !
  */
 class Statement
 {
@@ -176,7 +178,7 @@ private:
 
 private:
     sqlite3_stmt*   mpStmt;         //!< Pointer to SQLite Statement Object
-    unsigned int*   mpStmtRefCount; //!< Pointer to the reference counter of the Statement Object (to share it with Column objects)
+    unsigned int*   mpStmtRefCount; //!< Pointer to the heap allocated reference counter of the sqlite3_stmt (to share it with Column objects)
     sqlite3*        mpSQLite;       //!< Pointer to SQLite Database Connection Handle
     std::string     mQuery;         //!< UTF-8 SQL Query
     int             mColumnCount;   //!< Number of column in the result of the prepared statement