# Using the Flashlight (C++)

To use the flashlight mode, you manipulate your phone to turn on the flashlight, which then stays on persistently.

When you use the flashlight mode with a camera application, the following situations may occur:
- When the rear camera is used and [Camera_FlashMode](../../reference/apis-camera-kit/_o_h___camera.md#camera_flashmode) is set to off, the flashlight cannot be turned on.
- When the front camera is used, the flashlight can be turned on and remains steady on.
- When you switch from the front camera to the rear camera, the flashlight will be automatically turned off if it was turned on previously.

## How to Develop

Read [Camera](../../reference/apis-camera-kit/_o_h___camera.md) for the API reference.

1. Import the NDK.  

   ```c++
    // Include the NDK header files.
    #include "hilog/log.h"
    #include "ohcamera/camera.h"
    #include "ohcamera/camera_input.h"
    #include "ohcamera/capture_session.h"
    #include "ohcamera/camera_manager.h"
   ```

2. Link the dynamic library in the CMake script.

    ```txt
     target_link_libraies(entry PUBLIC libohcamera.so libhilog_ndk.z.so)
    ```

3. Call [OH_CameraManager_IsTorchSupported()](../../reference/apis-camera-kit/_o_h___camera.md#oh_cameramanager_istorchsupported) to check whether the current device supports the flashlight.

    ```c++
   // Check whether the device supports the flashlight.
   Camera_OutputCapability* cameraOutputCapability = nullptr;
   Camera_TorchMode torchMode = AUTO;
   bool isTorchSupported = false;
   Camera_ErrorCode ret = OH_CameraManager_IsTorchSupported(cameraManager, &isTorchSupported);
   if (cameraManager == nullptr || ret != CAMERA_OK) {
        OH_LOG_ERROR(LOG_APP, "OH_CameraManager_IsTorchSupported failed.");
   }
   if (isTorchSupported) {
        OH_LOG_INFO(LOG_APP, "isTorchSupported success.");
   } else {
        OH_LOG_ERROR(LOG_APP, "isTorchSupported failed.");
   }
   ```

4. Call [OH_CameraManager_IsTorchSupportedByTorchMode()](../../reference/apis-camera-kit/_o_h___camera.md#oh_cameramanager_istorchsupportedbytorchmode) to check whether the current device supports a specific flashlight mode.

   ```c++
   bool torchModeSupported = false;
   ret = OH_CameraManager_IsTorchSupportedByTorchMode(cameraManager, torchMode, &torchModeSupported);
   if (cameraManager == nullptr || ret != CAMERA_OK) {
        OH_LOG_ERROR(LOG_APP, "OH_CameraManager_IsTorchSupported failed.");
   }
   if (torchModeSupported) {
        OH_LOG_INFO(LOG_APP, "isTorchModeSupported success.");
   } else {
        OH_LOG_ERROR(LOG_APP, "isTorchModeSupported failed. %{public}d ", ret);
   }
   ```

5. Call [OH_CameraManager_SetTorchMode()](../../reference/apis-camera-kit/_o_h___camera.md#oh_cameramanager_settorchmode) to set the flashlight mode.

   ```c++
   if (torchModeSupported) {
      OH_LOG_INFO(LOG_APP, "OH_CameraManager_IsTorchModeSupported success.");
      // Set the flashlight mode.
      ret = OH_CameraManager_SetTorchMode(cameraManager, torchMode);
      if (ret != CAMERA_OK) {
          OH_LOG_ERROR(LOG_APP, "OH_CameraManager_SetTorchMode failed. %{public}d ", ret);
      } else {
          OH_LOG_INFO(LOG_APP, "OH_CameraManager_SetTorchMode success.");
        }
   } else {
      OH_LOG_ERROR(LOG_APP, "OH_CameraManager_IsTorchModeSupported failed.");
   }
   ```


## Status Listening

During camera application development, you can listen for changes of the flashlight status, including on, off, unavailable, and available, by using the callback function.

   Register the **'cameratorchStatusChange'** event and return the listening result through a callback, which carries the **Camera_TorchStatusInfo** parameter. For details about the parameter, see [Camera_TorchStatusInfo](../../reference/apis-camera-kit/_camera___torch_status_info.md).

   ```c++
   ret = OH_CameraManager_RegisterTorchStatusCallback(cameraManager, GetTorchStatusCb);
   if (ret != CAMERA_OK) {
      OH_LOG_ERROR(LOG_APP, "OH_CameraManager_RegisterTorchStatusCallback failed.");
   }
   ```
   ```c++
   void OnTorchStatusChange(Camera_Manager *cameraManager, Camera_TorchStatusInfo* torchStatus)
   {
      OH_LOG_INFO(LOG_APP, "OH_CameraManager_RegisterTorchStatusCallback is called.");
   }
   void GetTorchStatusCb(Camera_Manager *cameraManager, Camera_TorchStatusInfo* torchStatus)
   {
      OH_LOG_INFO(LOG_APP, "GetTorchStatusCb is called.");
   }
   ```