Writing a Hello World Program

The following exemplifies how to run the first program on the development board. The created program outputs the message "Hello World!"

Prerequisites

A project for the Hi3516 development board has been created as instructed in Creating a Project and Obtaining Source Code.

Example Directory

The complete code directory is as follows:

applications/sample/hello
│── BUILD.gn
└── src
    └── helloworld.c

How to Develop

Perform the steps below in the source code directory:

Create a directory and the program source code.

Create the applications/sample/hello/src/helloworld.c directory and file whose code is shown in the following example. You can customize the content to be printed. For example, you can change OHOS to World. You can use either C or C++ to develop a program.
```
#include <stdio.h>

int main(int argc, char **argv)
{
    printf("\n\n");
    printf("\n\t\tHello OHOS!\n");
    printf("\n\n\n");

    return 0;
}
```

Create a build file.

Create the applications/sample/hello/BUILD.gn file. The file content is as follows:

import("//build/lite/config/component/lite_component.gni")
lite_component("hello-OHOS") {
  features = [ ":helloworld" ]
}
executable("helloworld") {
  output_name = "helloworld"
  sources = [ "src/helloworld.c" ]
}

Add a component.

Modify the build/lite/components/applications.json file and add the configuration of hello_world_app. The following code snippet is a snippet of the applications.json file, where the configuration between ##start## and ##end## is the new entry. (The ##start## and ##end## lines are only used to identify the location. After the configuration is complete, delete these lines.)

NOTE

In this example, the OpenHarmony-v3.1-Release version is used, where the component configuration file is build/lite/components/applications.json. In OpenHarmony-v3.2-Beta2 and later versions, the component configuration file is build/lite/components/communication.json.

{
  "components": [
    {
      "component": "camera_sample_communication",
      "description": "Communication related samples.",
      "optional": "true",
      "dirs": [
        "applications/sample/camera/communication"
      ],
      "targets": [
        "//applications/sample/camera/communication:sample"
      ],
      "rom": "",
      "ram": "",
      "output": [],
      "adapted_kernel": [ "liteos_a" ],
      "features": [],
      "deps": {
        "components": [],
        "third_party": []
      }
    },
##start##
    {
      "component": "hello_world_app",
      "description": "hello world samples.",
      "optional": "true",
      "dirs": [
        "applications/sample/hello"
      ],
      "targets": [
        "//applications/sample/hello:hello-OHOS"
      ],
      "rom": "",
      "ram": "",
      "output": [],
      "adapted_kernel": [ "liteos_a" ],
      "features": [],
      "deps": {
        "components": [],
        "third_party": []
      }
    },
##end##
    {
      "component": "camera_sample_app",
      "description": "Camera related samples.",
      "optional": "true",
      "dirs": [
        "applications/sample/camera/launcher",
        "applications/sample/camera/cameraApp",
        "applications/sample/camera/setting",
        "applications/sample/camera/gallery",
        "applications/sample/camera/media"
      ],

Modify the board configuration file.

Modify the vendor/hisilicon/hispark_taurus/config.json file and add an entry for the hello_world_app component. The following code snippet is the configuration of the applications subsystem, where the configuration between ##start## and ##end## is the new entry. (The ##start## and ##end## lines are only used to identify the location. After the configuration is complete, delete these lines.)
```
      {
        "subsystem": "applications",
        "components": [
          { "component": "camera_sample_app", "features":[] },
          { "component": "camera_sample_ai", "features":[] },
##start##
          { "component": "hello_world_app", "features":[] },
##end##
          { "component": "camera_screensaver_app", "features":[] }
        ]
      },
```