1# Writing a Hello World Program 2 3 4The following exemplifies how to run the first program on the development board. The created program outputs the message "Hello World!". 5 6 7 8## Example Directory 9 10Obtain 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**. 11The complete code directory is as follows: 12 13 14``` 15sample/hello 16│── BUILD.gn 17│── include 18│ └── helloworld.h 19│── src 20│ └── helloworld.c 21├── bundle.json 22build 23└── subsystem_config.json 24vendor/hihope 25└── rk3568 26 └── config.json 27``` 28 29 30## How to Develop 31 32Perform the steps below in the source code root directory: 33 341. Create a directory and write the service code. 35 36 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**. The print function **HelloPrint** is declared in the included **helloworld.h** file. You can use either C or C++ to develop a program. 37 38 39 ``` 40 #include <stdio.h> 41 #include "helloworld.h" 42 43 int main(int argc, char **argv) 44 { 45 HelloPrint(); 46 return 0; 47 } 48 49 void HelloPrint() 50 { 51 printf("\n\n"); 52 printf("\n\t\tHello World!\n"); 53 printf("\n\n"); 54 } 55 ``` 56 57 Add the header file **sample/hello/include/helloworld.h**. The sample code is as follows: 58 59 60 ``` 61 #ifndef HELLOWORLD_H 62 #define HELLOWORLD_H 63 #ifdef __cplusplus 64 #if __cplusplus 65 extern "C" { 66 #endif 67 #endif 68 69 void HelloPrint(); 70 71 #ifdef __cplusplus 72 #if __cplusplus 73 } 74 #endif 75 #endif 76 #endif // HELLOWORLD_H 77 ``` 78 792. Create a build file. 80 81 Create the **sample/hello/BUILD.gn** file. For details, see [Module](../subsystems/subsys-build-module.md). 82 83 The content of the **BUILD.gn** file is as follows: 84 85 ``` 86 import("//build/ohos.gni") # Import the build template. 87 ohos_executable("helloworld") {# Executable module. 88 sources = [ # Source code of the module. 89 "src/helloworld.c" 90 ] 91 include_dirs = [ # Directory of header files on which the module depends. 92 "include" 93 ] 94 cflags = [] 95 cflags_c = [] 96 cflags_cc = [] 97 ldflags = [] 98 configs = [] 99 deps =[] # Internal dependencies of a component. 100 part_name = "hello" # Component name. This parameter is mandatory. 101 install_enable = true # Whether to install the software by default. This parameter is optional. By default, the software is not installed. 102 } 103 ``` 104 1053. Create a component configuration file. 106 107 Create the **sample/hello/bundle.json** file and add the **sample** component description therein. For details, see [Component](../subsystems/subsys-build-component.md). 108 109 The content of the **bundle.json** file is as follows: 110 111 ``` 112 { 113 "name": "@ohos/hello", 114 "description": "Hello world example.", 115 "version": "3.1", 116 "license": "Apache License 2.0", 117 "publishAs": "code-segment", 118 "segment": { 119 "destPath": "sample/hello" 120 }, 121 "dirs": {}, 122 "scripts": {}, 123 "component": { 124 "name": "hello", 125 "subsystem": "sample", 126 "syscap": [], 127 "features": [], 128 "adapted_system_type": [ "mini", "small", "standard" ], 129 "rom": "10KB", 130 "ram": "10KB", 131 "deps": { 132 "components": [], 133 "third_party": [] 134 }, 135 "build": { 136 "sub_component": [ 137 "//sample/hello:helloworld" 138 ], 139 "inner_kits": [], 140 "test": [] 141 } 142 } 143 } 144 ``` 145 146 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. Add the APIs provided for other components, if any, in **inner_kits**. Add the test cases, if any, in **test**. 147 1484. Modify the subsystem configuration file. 149 150 Add the configuration of the new subsystem to the **build/subsystem_config.json** file. For details, see [Subsystem](../subsystems/subsys-build-subsystem.md). 151 152 The configuration of the new subsystem is as follows: 153 154 ``` 155 "sample": { 156 "path": "sample", 157 "name": "sample" 158 }, 159 ``` 160 1615. Modify the product configuration file. 162 163 >  **NOTE** 164 > 165 > 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**. 166 167 - Versions earlier than OpenHarmony-v3.2-Beta2 168 169 In the **productdefine/common/products/rk3568.json** file, add the **hello** part after the existing part. 170 171 ``` 172 "usb:usb_manager_native":{}, 173 "applications:prebuilt_hap":{}, 174 "sample:hello":{}, 175 "wpa_supplicant-2.9:wpa_supplicant-2.9":{}, 176 ``` 177 178 - OpenHarmony-v3.2-Beta2 and later versions 179 180 181 In the **vendor/hihope/rk3568/config.json** file, add the **hello** part after the existing part. 182 183 ``` 184 { 185 "subsystem": "sample", 186 "components": [ 187 { 188 "component": "hello", 189 "features": [] 190 } 191 ] 192 }, 193 ``` 194
