Merge branch 'doc/minor_cxx_additions' into 'master'

doc: small changes for cxx code style

See merge request espressif/esp-idf!7210

docs/en/contribute/style-guide.rst

@@ -194,7 +194,7 @@ The same rules as for C apply. Where they are not enough, apply the following ru
 
 File Naming
 ^^^^^^^^^^^^
-C++ Header files have the extension ``.h``. C++ source files have the extension ``.cpp``, which is important for the compiler to distiguish them from normal C source files.
+C++ Header files have the extension ``.hpp``. C++ source files have the extension ``.cpp``. The latter is important for the compiler to distiguish them from normal C source files.
 
 Naming
 ^^^^^^
@@ -202,11 +202,39 @@ Naming
 * **Class and struct** names shall be written in ``CamelCase`` with a capital letter as beginning. Member variables and methods shall be in ``snake_case``.
 * **Namespaces** shall be in lower ``snake_case``.
 * **Templates** are specified in the line above the function declaration.
+* Interfaces in terms of Object-Oriented Programming shall be named without the suffix ``...Interface``. Later, this makes it easier to extract interfaces from normal classes and vice versa without making a breaking change.
 
 Member Order in Classes
 ^^^^^^^^^^^^^^^^^^^^^^^
+In order of precedence:
 
-First put the public members, then the protected, then private ones. Omit public, protected or private sections without any members.
+* First put the public members, then the protected, then private ones. Omit public, protected or private sections without any members.
+* First put constructors/destructors, then member functions, then member variables.
+
+For example:
+
+::
+
+    class ForExample {
+    public:
+        // first constructors, then default constructor, then destructor
+        ForExample(double example_factor_arg);
+        ForExample();
+        ~ForExample();
+
+        // then remaining pubic methods
+        set_example_factor(double example_factor_arg);
+
+        // then public member variables
+        uint32_t public_data_member;
+
+    private:
+        // first private methods
+        void internal_method();
+
+        // then private member variables
+        double example_factor;
+    };
 
 Spacing
 ^^^^^^^