#112 Update Dockerfiles and README to explain the presence of two environments...

#112 Update Dockerfiles and README to explain the presence of two environments and use the correct one to generate Docker images.

README.md

@@ -66,12 +66,23 @@ Should the procedure described below not work at some point I invite you to chec
 * Create a new conda environment and activate it:
 
 ```shell
-conda env create -f environment.yml
+conda env create -f environment_local.yml
 conda activate training_cpp
 ```
 
 Don't forget to activate it each time you intend to run the lecture!
 
+**Note** We had to define two environments:
+- One that seems to work on recent Ubuntu and in docker image creation, with gcc set at version 9.4.
+- Another that set gcc at 10.4 for Binder - the v9.4 fails completely.
+
+The 10.4 in local resulted in errors while using C++ 14 ou C++ 17 standards in notebook (and is in issues from Xeus-cling project).
+
+This underlines Xeus-cling is not under active development and is not properly maintained; we'll have to cope with it until we [find another solution](https://gitlab.inria.fr/formations/cpp/gettingstartedwithmoderncpp/-/issues/101) for this training.
+
+If none works for you please consider using an existing Docker image or Binder.
+
+
 * Then you can run the notebook by going **into its root directory** (or internal links won't work...) in a terminal and typing:
 
 ```shell

docker/Dockerfile.xeus-cling

@@ -11,8 +11,8 @@ USER ${USER}
 
 # Create the environment:
 WORKDIR /home/${USER}/training_cpp
-COPY environment.yml .
-RUN conda env create -f environment.yml 
+COPY environment_local.yml .
+RUN conda env create -f environment_local.yml 
 
 # Make RUN commands use the new environment:
 SHELL ["/bin/bash", "-c"] 

docker/Dockerfile.xeus-cling_with_compilers

@@ -38,8 +38,8 @@ WORKDIR /home/${USER}
 
 # Create the environment:
 WORKDIR /home/${USER}/gettingstartedwithmoderncpp
-COPY environment.yml .
-RUN /home/${USER}/miniconda3/bin/conda env create -f environment.yml
+COPY environment_local.yml .
+RUN /home/${USER}/miniconda3/bin/conda env create -f environment_local.yml
 RUN /home/${USER}/miniconda3/bin/conda clean -a
 
 # Change the default shell to be bash