The IDL (Interface Definition Language) file is the component's definition. It contains the functions the component exposes and the interface it must implement, regardless of the language in which is implemented.

In this link you can find more info about IDL syntax and definitions.

Set IDL for our hello-world components

For any given component we have to follow 3 steps:

1. Implement component's IDL
2. Implement component
3. Install component in ACS

So, we create the component's IDL directory and file:

cd ~/workspace
getTemplateForDirectory MODROOT_WS idlHelloComp
cd idlHelloComp/src
touch ../idl/HelloComponent.idl
vim ../idl/HelloComponent.idl

We fill the IDL with the following:

#ifndef _HELLOCOMPONENT_IDL_
#define _HELLOCOMPONENT_IDL_

#pragma prefix "acsws"

#include <acscomponent.idl>

module workshop {
    interface HelloComponent : ACS::ACSComponent {
        string printHello();
    };
};

#endif

We add our component's IDL to the Makefile:

vim ~/workspace/idlHelloComp/src/Makefile

...
IDL_FILES = HelloComponent
HelloComponentStubs_LIBS = acscomponentStubs
...
COMPONENT_HELPERS=on
...

We then compile and install the IDL definitions:

make all
make install