Writing a Hello World Program

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

Prerequisites

A project for the RK3568 development board has been created as instructed in Creating a Project and Obtaining Source Code.

Example Directory

Obtain the OpenHarmony project code. From the source code root directory, add the sample/hello directory, and then create therein the hello source code directory, the build file BUILD.gn, and the component configuration file bundle.json. The complete code directory is as follows:

sample/hello
│── BUILD.gn
│── include
│   └── helloworld.h
│── src
│   └── helloworld.c
├── bundle.json
build
└── subsystem_config.json
vendor/hihope
└── rk3568
    └── config.json

How to Develop

Perform the steps below in the source code directory:

Create a directory and write the service code.

Create the sample/hello/src/helloworld.c file, with the sample code as follows. In this example, the content to be printed is World, which you can change to any string that you prefer, for example, OHOS. Declare the string printing function HelloPrint in the helloworld.h file. You can use either C or C++ to develop a program.

#include <stdio.h>
#include "helloworld.h"

int main(int argc, char **argv)
{
    HelloPrint();
    return 0;
}

void HelloPrint()
{
    printf("\n\n");
    printf("\n\t\tHello World!\n");
    printf("\n\n");
}

Add the header file sample/hello/include/helloworld.h. The sample code is as follows:

#ifndef HELLOWORLD_H
#define HELLOWORLD_H
#ifdef __cplusplus
#if __cplusplus
extern "C" {
#endif
#endif

void HelloPrint();

#ifdef __cplusplus
#if __cplusplus
}
#endif
#endif
#endif // HELLOWORLD_H

Create a build file.

Create the sample/hello/BUILD.gn file. For details, see Module.

The content of the BUILD.gn file is as follows:

import("//build/ohos.gni") # Import the build template.
ohos_executable("helloworld") {# Executable module.
  sources = [       # Source code of the module.
    "src/helloworld.c"
  ]
  include_dirs = [  # Directory of header files on which the module depends.
    "include" 
  ]
  cflags = []
  cflags_c = []
  cflags_cc = []
  ldflags = []
  configs = []
  deps =[]    # Internal dependencies of a component.
  part_name = "hello"    # Component name. This parameter is mandatory.
  install_enable = true # Whether to install the software by default. This parameter is optional. By default, the software is not installed.
}

Create a component configuration file.

Create the sample/hello/bundle.json file and add the sample component description therein. For details, see Component.

The content of the bundle.json file is as follows:

{
    "name": "@ohos/hello",
    "description": "Hello world example.",
    "version": "3.1",
    "license": "Apache License 2.0",
    "publishAs": "code-segment",
    "segment": {
        "destPath": "sample/hello"
    },
    "dirs": {},
    "scripts": {},
    "component": {
        "name": "hello",
        "subsystem": "sample",
        "syscap": [],
        "features": [],
        "adapted_system_type": [ "mini", "small", "standard" ],
        "rom": "10KB",
        "ram": "10KB",
        "deps": {
            "components": [],
            "third_party": []
        },
        "build": {
            "sub_component": [
                "//sample/hello:helloworld"
            ],
            "inner_kits": [],
            "test": []
        }
    }
}

The bundle.json file consists of two parts. The first part describes the information about the subsystem to which the component belongs, and the second part defines the build configuration for the component. When adding a component, you must specify the sub_component of the component. If there are APIs provided for other components, add them in inner_kits. If there are test cases, add them in test.

Modify the subsystem configuration file.

Add the configuration of the new subsystem to the build/subsystem_config.json file. For details, see Subsystem.

The configuration of the new subsystem is as follows:
```
"sample": {
    "path": "sample",
    "name": "sample"
  },
```
Modify the product configuration file.

NOTE

In versions earlier than OpenHarmony-v3.2-Beta2, the RK3568 configuration file is productdefine/common/products/rk3568.json. In OpenHarmony-v3.2-Beta2 and later versions, the RK3568 configuration file is vendor/hihope/rk3568/config.json.
- Versions earlier than OpenHarmony-v3.2-Beta2
  
  In the productdefine/common/products/rk3568.json file, add the hello part after the existing part.
```
"usb:usb_manager_native":{},
"applications:prebuilt_hap":{},
"sample:hello":{},
"wpa_supplicant-2.9:wpa_supplicant-2.9":{},
```
- OpenHarmony-v3.2-Beta2 and later versions
  
  In the vendor/hihope/rk3568/config.json file, add the hello part after the existing part.
```
{
  "subsystem": "sample",
  "components": [
    {
      "component": "hello",
      "features": []
    }
  ]
},     
```