Build and run the C++ Hello World component{:.external} included in the SDK samples repository. Components are the basic unit of executable software on Fuchsia.

The tasks include:

• Build and run the sample Hello World component.
• Make a change to the component.
• Repeat the build and run steps.
• Verify the change.

Do the following:

1. Build and run the sample component:

   tools/bazel run //src/hello_world:pkg.component
   

   When the build is successful, this command generates build artifacts in a temporary Fuchsia package repository, which is then removed after the component runs.

   The command prints output similar to the following:

   $ tools/bazel run //src/hello_world:pkg.component
   ...
   INFO: Build completed successfully, 155 total actions
   Running workflow: pkg.component_base
   Running task: pkg.debug_symbols_base (step 1/2)
   Running task: pkg.component.run_base (step 2/2)
   added repository bazel.pkg.component.runnable
   URL: fuchsia-pkg://bazel.pkg.component.runnable/hello_world#meta/hello_world.cm
   Moniker: /core/ffx-laboratory:hello_world.cm
   Creating component instance...
   Resolving component instance...
   Starting component instance...
   Started component instance!
   

2. Check the status of the hello_world component:

   tools/ffx component show hello_world
   

   This command prints output similar to the following:

   $ tools/ffx component show hello_world
                  Moniker:  /core/ffx-laboratory:hello_world.cm
                      URL:  fuchsia-pkg://bazel.pkg.component.runnable/hello_world#meta/hello_world.cm
              Instance ID:  None
                     Type:  CML Component
          Component State:  Resolved
    Incoming Capabilities:  /svc/fuchsia.logger.LogSink
     Exposed Capabilities:
              Merkle root:  eebd529bd8ac6d2fd8a467279719f74c76643ebee2e94ebf594ffcbaac02fe8f
          Execution State:  Stopped
   

   The output shows that the hello_world component has run and is now terminated (Stopped).

3. Verify the Hello, World! message in the device logs:

   tools/ffx log --filter hello_world dump
   

   This command prints output similar to the following:

   $ tools/ffx log --filter hello_world dump
   [2022-11-30 02:32:28.122][<ffx>]: logger started.
   [183.252][pkg-resolver][pkg-resolver][I] updated local TUF metadata for "fuchsia-pkg://bazel.pkg.component.runnable" to version RepoVersions { root: 1, timestamp: Some(1669775711), snapshot: Some(1669775711), targets: Some(1669775711) } while getting merkle for TargetPath("hello_world/0")
   [183.347][pkg-resolver][pkg-resolver][I] resolved fuchsia-pkg://bazel.pkg.component.runnable/hello_world as fuchsia-pkg://bazel.pkg.component.runnable/hello_world to eebd529bd8ac6d2fd8a467279719f74c76643ebee2e94ebf594ffcbaac02fe8f with TUF
   [183.362][pkg-resolver][pkg-resolver][I] resolved fuchsia-pkg://bazel.pkg.component.runnable/hello_world as fuchsia-pkg://bazel.pkg.component.runnable/hello_world to eebd529bd8ac6d2fd8a467279719f74c76643ebee2e94ebf594ffcbaac02fe8f with TUF
   {{ '<strong>' }}[183.397][ffx-laboratory:hello_world.cm][I] Hello, World!{{ '</strong>' }}
   

4. Use a text editor to edit the src/hello_world/hello_world.cc file, for example:

   nano src/hello_world/hello_world.cc
   

5. Change the message to "Hello again, World!".

   The main() method now should look like below:

   int main() {
     {{ '<strong>' }}std::cout << "Hello again, World!\n";{{ '</strong>' }}
     return 0;
   }
   

6. Save the file and exit the text editor.

7. Build and run the sample component again:

   tools/bazel run //src/hello_world:pkg.component
   

8. Verify the Hello again, World! message in the device logs:

   tools/ffx log --filter hello_world dump
   

   This command prints output similar to the following;

   $ tools/ffx log --filter hello_world dump
   ...
   [280.088][pkg-resolver][pkg-resolver][I] resolved fuchsia-pkg://bazel.pkg.component.runnable/hello_world as fuchsia-pkg://bazel.pkg.component.runnable/hello_world to 03405c9f712b2db800194d496ce90372845a8f4bbcb1df4a9abfe9c5bdfc40fb with TUF
   {{ '<strong>' }}[280.113][ffx-laboratory:hello_world.cm][I] Hello again, World!{{ '</strong>' }}