## 1. Failed to run the KV store on the LiteOS Cortex-A kernel \(Hi3516 or Hi3518\) due to incorrect path setting for the KV store<a name="section2041345718513"></a>
**Symptom**
When the LiteOS Cortex-A kernel \(Hi3516 or Hi3518 platform\) directly calls the API provided by the KV store, the compiled executable program fails to run.
**Possible Causes**
The compiled executable program is run directly without being converted to an application using **AbilityKit** APIs. In this case, the Bundle Manager Service \(BMS\) cannot correctly set the path for storing application data during application installation. As a result, the KV store fails to run.
**Solution**
Call the **UtilsSetEnv** function of the KV store to set the data storage path.
## Available APIs<a name="section1633115419401"></a>
**Table 1** APIs for file operations
| Function | Description |
| ---------- | ------------- |
| int UtilsFileOpen(const char* path, int oflag, int mode) | Opens or creates a file. |
| int UtilsFileClose(int fd) | Closes a file with a specified file descriptor. |
| int UtilsFileRead(int fd, char *buf, unsigned int len) | Reads a specified length of data from a file with the specified file descriptor and writes the data into the buffer. |
| int UtilsFileWrite(int fd, const char *buf, unsigned int len) | Writes a specified length of data into a file with the specified file descriptor. |
| int UtilsFileDelete(const char *path) | Deletes a specified file. |
| int UtilsFileStat(const char *path, unsigned int *fileSize) | Obtains the file size. |
| int UtilsFileSeek(int fd, int offset, unsigned int whence) | Adjusts the read and write position offset in a file. |
| int UtilsFileCopy(const char* src, const char* dest) | Copies the source file to a target file. |
| int UtilsFileMove(const char* src, const char* dest) | Moves the source file into a target file. |
int fd = UtilsFileOpen(fileName, O_RDWR_FS | O_CREAT_FS | O_TRUNC_FS, 0);
printf("file handle = %d\n", fd);
int ret = UtilsFileWrite(fd, def, strlen(def));
printf("write ret = %d\n", ret);
// Adjust the position offset in the file.
ret = UtilsFileSeek(fd, 5, SEEK_SET_FS);
printf("lseek ret = %d\n", ret);
// Read data and close the file.
char buf[64] = {0};
int readLen = UtilsFileRead(fd, buf, 64);
ret = UtilsFileClose(fd);
printf("read len = %d : buf = %s\n", readLen, buf);
// Obtain the file size.
int fileLen = 0;
ret = UtilsFileStat(fileName, &fileLen);
printf("file size = %d\n", fileLen);
// Delete the file.
ret = UtilsFileDelete(fileName);
printf("delete ret = %d\n", ret);
```
**Table 2** APIs for KV store operations
| Function | Description |
| ----------- | ---------------- |
| int UtilsGetValue(const char* key, char* value, unsigned int len) | Obtains the value matching a specified key from the file system or cache. |
| int UtilsSetValue(const char* key, const char* value) | Adds or updates the value matching a specified key in the file system or cache. |
| int UtilsDeleteValue(const char* key) | Deletes the value matching a specified key from the file system or cache. |
Sample code for the KV store:
# Commonlibrary Development Guidelines<a name="EN-US_TOPIC_0000001059307279"></a>
## Overview
The **commonlibrary** subsystem stores basic OpenHarmony components which provides common enhanced APIs for development in C, C++ and JS that are commonly used by OpenHarmony service subsystems and upper-layer applications. Including repositories:
```
// Set the value matching the specified key.
char key[] = "rw.sys.version_100";
char value[] = "Hello kv operation implement!";
int ret = UtilsSetValue(key, value);
printf("UtilsSetValue set ret = %d\n", ret);
// Obtain the value matching the specified key.
char temp[128] = {0};
ret = UtilsGetValue(key, temp, 128);
printf("UtilsGetValue get ret = %d, temp = %s\n", ret, temp);
// Delete the value matching the specified key.
ret = UtilsDeleteValue(key);
printf("UtilsDeleteValue delete ret = %d\n", ret);
/commonlibrary
├── c_utils # Enhanced basic C/C++ library for developers
├── ets_utils # Enhanced basic JS library for developers
└── utils_lite # Basic tools for liteOS, including C and JS.
```
Features provided by every repositories are listed here:
## How to Develop<a name="section17450172710292"></a>
### Developing a Native Application for the KV Store That Uses the LiteOS Cortex-A Kernel \(Hi3516 or Hi3518\)<a name="section258354119295"></a>
1. Develop the native application for the KV store using **AbilityKit** APIs.
- Write the user program by calling the APIs provided by the KV store and compile the **libLauncher.so** file.
```
// Set the value matching the specified key.
char key[] = "rw.sys.version_100";
char value[] = "Hello kv operation implement!";
int ret = UtilsSetValue(key, value);
printf("UtilsSetValue set ret = %d\n", ret);
// Obtain the value matching the specified key.
char temp[128] = {0};
ret = UtilsGetValue(key, temp, 128);
printf("UtilsGetValue get ret = %d, temp = %s\n", ret, temp);
// Delete the value matching the specified key.
ret = UtilsDeleteValue(key);
printf("UtilsDeleteValue delete ret = %d\n", ret);
- Add resource files in the **res/drawable** directory based on the following directory structure.
- Compress the **libLauncher.so**, **config.json**, and resource files into a ZIP package and change the file name extension to **.hap**, for example, **Launcher.hap**.
2. Connect the development board and send the command for installing the native KV store application to the board through the serial port.
See [Development Guidelines for c_utils](https://gitee.com/openharmony/commonlibrary_c_utils/blob/master/docs/en/c-utils-guide.md), including FAQs for several scenarios.
The **commonlibrary** subsystem provides common enhanced APIs for development in C, C++ and JS.
The **commonlibrary** subsystem stores basic OpenHarmony components which provides common enhanced APIs for development in C, C++ and JS that are commonly used by OpenHarmony service subsystems and upper-layer applications. Including repositories:
```
/commonlibrary
├── c_utils # Enhanced basic C/C++ library for developers
├── ets_utils # Enhanced basic JS library for developers
└── utils_lite # Basic tools for liteOS, including C and JS.
```
Features provided by every repositories are listed here:
**c_utils**
...
...
@@ -24,15 +31,8 @@ The **commonlibrary** subsystem provides common enhanced APIs for development in
- Hardware Abstraction Layer (HAL) APIs for performing operations on standard files
