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# Native APIs
- [Using Native APIs in Application Projects](napi-guidelines.md)
- [Raw File Development](rawfile-guidelines.md)
# Raw File Development
## When to Use
This document describes how to use the native Rawfile APIs to manage raw file directories and files in OpenHarmony. The table below describes the APIs.
## Available APIs
| API | Description |
| :----------------------------------------------------------- | :--------------------------------------- |
| NativeResourceManager *OH_ResourceManager_InitNativeResourceManager(napi_env env, napi_value jsResMgr) | Initializes the native resource manager. |
| RawDir *OH_ResourceManager_OpenRawDir(const NativeResourceManager *mgr, const char *dirName) | Opens a raw file directory. |
| int OH_ResourceManager_GetRawFileCount(RawDir *rawDir) | Obtains the number of raw files in the specified directory.|
| const char *OH_ResourceManager_GetRawFileName(RawDir *rawDir, int index) | Obtains the name of a raw file. |
| RawFile *OH_ResourceManager_OpenRawFile(const NativeResourceManager *mgr, const char *fileName) | Opens a raw file. |
| long OH_ResourceManager_GetRawFileSize(RawFile *rawFile) | Obtains the size of a raw file. |
| int OH_ResourceManager_SeekRawFile(const RawFile *rawFile, long offset, int whence) | Seeks a data read/write position in a raw file based on the specified offset. |
| long OH_ResourceManager_GetRawFileOffset(const RawFile *rawFile) | Obtains the offset. |
| int OH_ResourceManager_ReadRawFile(const RawFile *rawFile, void *buf, size_t length) | Reads a raw file. |
| void OH_ResourceManager_CloseRawFile(RawFile *rawFile) | Closes a raw file to release resources. |
| void OH_ResourceManager_CloseRawDir(RawDir *rawDir) | Closes a raw file directory to release resources. |
| bool OH_ResourceManager_GetRawFileDescriptor(const RawFile *rawFile, RawFileDescriptor &descriptor) | Obtains the file description (FD) of a raw file. |
| bool OH_ResourceManager_ReleaseRawFileDescriptor(const RawFileDescriptor &descriptor) | Releases the FD of a raw file. |
| void OH_ResourceManager_ReleaseNativeResourceManager(NativeResourceManager *resMgr) | Releases native resource manager resources. |
## How to Develop
1. Add the header file.
```c++
#include "raw_file_manager.h"
```
2. Call **OH_ResourceManager_InitNativeResourceManager(napi_env env, napi_value jsResMgr)** to obtain a **NativeResourceManager** instance.
```js
// Call the JS API to pass the JS resource manager.
import resManager from '@ohos.resourceManager'
import rawfileTest from 'librawFileTest.so'
resManager.getResourceManager().then(resmgr => {
rawfileTest.testRawFile("test", resmgr, (error, value) => {
console.log("test rawFile");
})
});
```
```c++
// The C++ API obtains and parses the parameters passed by the JS API.
NativeResourceManager* nativeResourceManager = nullptr;
std::string path;
if (i == 0 && valueType == napi_string) {
// Parse the first parameter, which is the file or directory path relative to the raw file directory.
......
path = buf.data();
} else if (i == 1 && valueType == napi_object) {
// Parse the second parameter, which is the resource manager.
nativeResourceManager = OH_ResourceManager_InitNativeResourceManager(env, argv[i]);
}
```
3. Call **OH_ResourceManager_OpenRawDir** to obtain a **RawDir** instance based on the **NativeResourceManager** instance.
```c++
RawDir* rawDir = OH_ResourceManager_OpenRawDir(nativeResourceManager, path.c_str());
```
4. Call **OH_ResourceManager_GetRawFileCount** to obtain the total number of raw files in the directory based on the **RawDir** instance.
```c++
int count = OH_ResourceManager_GetRawFileCount(rawDir);
```
5. Call **OH_ResourceManager_GetRawFileName** to obtain the name of the raw file based on the specified index.
```c++
for (int index = 0; index < count; index++) {
std::string fileName = OH_ResourceManager_GetRawFileName(rawDir, index);
}
```
6. Call **OH_ResourceManager_OpenRawFile** to obtain a **RawFile** instance based on the specified file name.
```c++
RawFile* rawFile = OH_ResourceManager_OpenRawFile(nativeResourceManager, fileName.c_str());
```
7. Call **OH_ResourceManager_GetRawFileSize** to obtain the size of the raw file.
```c++
long rawFileSize = OH_ResourceManager_GetRawFileSize(rawFile);
```
8. Call **OH_ResourceManager_SeekRawFile** to seek a data read/write position in the raw file based on the specified offset.
```c++
int position = OH_ResourceManager_SeekRawFile(rawFile, 10, 0);
int position = OH_ResourceManager_SeekRawFile(rawFile, 0 , 1);
int position = OH_ResourceManager_SeekRawFile(rawFile, -10, 2);
```
9. Call **OH_ResourceManager_GetRawFileOffset** to obtain the raw file offset.
```c++
long rawFileOffset = OH_ResourceManager_GetRawFileOffset(rawFile)
```
10. Call **OH_ResourceManager_ReadRawFile** to read a raw file.
```c++
std::unique_ptr<char[]> mediaData = std::make_unique<char[]>(rawFileSize);
long rawFileOffset = OH_ResourceManager_ReadRawFile(rawFile, mediaData.get(), rawFileSize);
```
11. Call **OH_ResourceManager_CloseRawFile** to close the file to release resources.
```c++
OH_ResourceManager_CloseRawFile(rawFile);
```
12. Call **OH_ResourceManager_CloseRawDir** to close the raw file directory.
```c++
OH_ResourceManager_CloseRawDir(rawDir);
```
13. Call **OH_ResourceManager_GetRawFileDescriptor** to obtain **RawFileDescriptor** of the raw file.
```c++
RawFileDescriptor descriptor;
bool result = OH_ResourceManager_GetRawFileDescriptor(rawFile, descriptor);
```
14. Call **OH_ResourceManager_ReleaseRawFileDescriptor** to release the FD of the raw file.
```c++
OH_ResourceManager_ReleaseRawFileDescriptor(descriptor);
```
15. Call **OH_ResourceManager_ReleaseNativeResourceManager** to release the native resource manager.
```c++
OH_ResourceManager_ReleaseNativeResourceManager(nativeResourceManager);
```
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