Creating GDS variables - Part 2 - The PLCnext Runtime

Creating GDS variables - Part 2

Now that we have seen how the PLCnext CLI can help us, let's use it to create a project containing an ACF component that creates some GDS variables.

Create a new project on the host system:

$ plcncli new acfproject --name MyGdsProject --namespace MyNamespace --component MyComponent --verbose

Set the build target for the project:
```
$ cd MyGdsProject
$ plcncli set target --add --name AXCF2152 --version 2021.9
```
If the target is ambiguous or cannot be found, you can use the following command to see the list of installed targets that the PLCnext CLI knows about:
```
$ plcncli get targets
```

Edit the source code using your favourite editor. In this case we will use Visual Studio Code:

$ code .

You can see that the PLCnext CLI has created the following source and configuration files in the MyGdsProject directory:

├── CMakeLists.txt
├── external
│   └── ADD_DEPENDENT_LIBRARIES_HERE.txt
├── How_to_deploy.txt
├── plcnext.proj
└── src
    ├── MyComponent.cpp
    ├── MyComponent.hpp
    └── MyGdsProjectLibrary.acf.config

Add a GDS variable to the section indicated in the component .hpp file:
```
//#port
Arp::uint8 MyGdsVariable;
```
GDS variables are also referred to as "ports". The PLCnext Info Center provides detailed information on GDS port definitions in C++ code, including the attributes that can be applied to GDS ports defined in this way.
Change the .acf.config file if necessary, e.g. the path to the shared object library file.
Save the edited file(s)
On the command-line, use the PLCnext CLI to generate the intermediate files for the project:

$ plcncli generate code --verbose

You can see that the PLCnext CLI has now created a lot of files in the MyGdsProject directory, including the following:
```
├── intermediate
│   └── code
│       ├── MyComponent.meta.cpp
│       ├── MyGdsProjectLibrary.cpp
│       ├── MyGdsProjectLibrary.hpp
│       └── MyGdsProjectLibrary.meta.cpp
```
These C++ source files contain additional code required for the PLCnext runtime to create instances of the C++ component and its GDS port(s).
Build the project:
```
$ plcncli build --verbose
```
This command uses CMake to build the project for all the specified targets.
Deploy the shared object library and the .acf.config file to the PLC as you've done previously.
Restart the PLCnext Runtime.

Your ACF component instance now includes a GDS port in the Global Data Space that can be accessed by other components using the Data Access RSC service.