Globally set C++ source block header arguments

Question

I try to globally set header properties for C++ source examples, with no success. I would have expected that the following works

 #+PROPERTY: header-args:C++ :var x=1.0

What did work is using general header args property:

 #+PROPERTY: header-args :var x=1.1

Also specific property drawer worked:

* Resources
:PROPERTIES:
:header-args:C++: :var x=1.2
:END:

And of course using plain old header arguments works:

#+header: :exports results
#+header: :includes <iostream>
#+header: :var x=1.3
#+begin_src C++
std::cout << x;
#+end_src

Could that be a bug or am I doing something wrong?

Answer 1

I found out, that I have to use cpp instead of C++ to get it working:

#+PROPERTY: header-args:cpp :var x=1.0

#+header: :exports results
#+header: :includes <iostream>
#+begin_src cpp
std::cout << x;
#+end_src

Reason: A single plus behind the property name means: Append the following property values to the already set ones. So the line

 #+PROPERTY: header-args:C++ :var x=1.0

is interpreted as: Append the value :var x=1.0 to the value of property header-args:C+.