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!" .

Example Directory

The complete code directory is as follows:

applications/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 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 World to OH. 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 applications/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 applications/sample/hello/BUILD.gn file. The file content 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 file 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 the applications/sample/hello/bundle.json file and add the description of the sample component. The content is as follows:

{
    "name": "@ohos/hello",
    "description": "Hello world example.",
    "version": "3.1",
    "license": "Apache License 2.0",
    "publishAs": "code-segment",
    "segment": {
        "destPath": "applications/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": [
                "//applications/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 component building configuration. When adding a part, you need to specify the sub_component contained in the part. If there are interfaces provided for other components, describe them in inner_kits. If there are test cases, describe them in test.

Modify the subsystem configuration file.

Add the configuration of the new subsystem to the build/subsystem_config.json file.
```
"sample": {
    "path": "applications/sample/hello",
    "name": "sample"
  },
```

Modify the product configuration file.

In the vendor\hihope\rk3568\config.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":{},