我正在研究学生信息系统，以便我有这个结构来存储学生信息：
ngOnInit() {
this.uploadService.getFileUploads().subscribe(result=>{
this.fileUploads = result;
});
}
我也做了这个排序功能：
struct student_info
{
string name;
int id;
string course;
int percent;
};
在这里，我从文件中读取并存储在struct中，将其推入struct的向量中，然后对其进行排序：
bool sorting(const container &a, const container &b) {
return a.percent < b.percent;
}
然后，我在某个地方看到了这个，但它没有清楚地解释为什么我不需要括号，即使排序是一个函数，为什么它只是student_info raw_data;
vector <student_info> container;
ifstream infile("data.txt");
while(!infile.eof())
{
infile >> raw_data.name >> raw_data.id >> raw_data.course >> raw_data.percent;
container.push_back(raw_data);
}
sort(container.begin(), container.end(), sorting);
而不是sorting当调用sort时？
答案 0 :(得分：3)
该函数的名称为private static final int SENSOR_ORIENTATION_DEFAULT_DEGREES = 90;
private static final int SENSOR_ORIENTATION_INVERSE_DEGREES = 270;
private static final SparseIntArray DEFAULT_ORIENTATIONS = new SparseIntArray();
private static final SparseIntArray INVERSE_ORIENTATIONS = new SparseIntArray();
private static final long DELAY = 1000;
long timeInMilliseconds = 0L;
long timeSwapBuff = 0L;
long updatedTime = 0L;
private long startTime = 0L;
int num = 1;
List<VideoModel> videoList;
private Handler customHandler = new Handler();
private static final String TAG = "RecordVideoActivity";
private String videoName;
static {
DEFAULT_ORIENTATIONS.append(Surface.ROTATION_0, 90);
DEFAULT_ORIENTATIONS.append(Surface.ROTATION_90, 0);
DEFAULT_ORIENTATIONS.append(Surface.ROTATION_180, 270);
DEFAULT_ORIENTATIONS.append(Surface.ROTATION_270, 180);
}
static {
INVERSE_ORIENTATIONS.append(Surface.ROTATION_0, 270);
INVERSE_ORIENTATIONS.append(Surface.ROTATION_90, 180);
INVERSE_ORIENTATIONS.append(Surface.ROTATION_180, 90);
INVERSE_ORIENTATIONS.append(Surface.ROTATION_270, 0);
}
private AutoFitTextureView mTextureView;
private ImageButton mRecordButton;
private ImageView mDots;
private ImageButton mCheckPoint;
private CameraDevice mCameraDevice;
private CameraCaptureSession mPreviewSession;
private TextureView.SurfaceTextureListener mSurfaceTextureListener
= new TextureView.SurfaceTextureListener() {
@Override
public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture,
int width, int height) {
openCamera(width, height);
}
@Override
public void onSurfaceTextureSizeChanged(SurfaceTexture surfaceTexture,
int width, int height) {
configureTransform(width, height);
}
@Override
public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
return true;
}
@Override
public void onSurfaceTextureUpdated(SurfaceTexture surfaceTexture) {
}
};
private Size mPreviewSize;
private Size mVideoSize;
private MediaRecorder mMediaRecorder;
private boolean mIsRecordingVideo;
private HandlerThread mBackgroundThread;
private Handler mBackgroundHandler;
private Semaphore mCameraOpenCloseLock = new Semaphore(1);
private CameraDevice.StateCallback mStateCallback = new CameraDevice.StateCallback() {
@Override
public void onOpened(@NonNull CameraDevice cameraDevice) {
mCameraDevice = cameraDevice;
startPreview();
mCameraOpenCloseLock.release();
if (null != mTextureView) {
configureTransform(mTextureView.getWidth(), mTextureView.getHeight());
}
}
@Override
public void onDisconnected(@NonNull CameraDevice cameraDevice) {
mCameraOpenCloseLock.release();
cameraDevice.close();
mCameraDevice = null;
}
@Override
public void onError(@NonNull CameraDevice cameraDevice, int error) {
mCameraOpenCloseLock.release();
cameraDevice.close();
mCameraDevice = null;
finish();
}
};
private Integer mSensorOrientation;
private String mNextVideoAbsolutePath;
private CaptureRequest.Builder mPreviewBuilder;
private CameraManager manager;
private String cameraId;
private boolean isFlashSupported;
private ImageButton flashButton;
private ImageButton switchCamera;
private ImageButton revertVideo;
public static final String CAMERA_BACK = "0";
private TextView mChronometer;
private String flashOpt;
private long lastSavedTime;
private String prepend;
private static Size chooseVideoSize(Size[] choices) {
for (Size size : choices) {
if (size.getWidth() == size.getHeight() * 4 / 3 && size.getWidth() <= 1080) {
return size;
}
}
Log.e(TAG, "Couldn't find any suitable video size");
return choices[choices.length - 1];
}
private static Size chooseOptimalSize(Size[] choices, int width, int height, Size aspectRatio) {
// Collect the supported resolutions that are at least as big as the preview Surface
List<Size> bigEnough = new ArrayList<>();
int w = aspectRatio.getWidth();
int h = aspectRatio.getHeight();
for (Size option : choices) {
if (option.getHeight() == option.getWidth() * h / w &&
option.getWidth() >= width && option.getHeight() >= height) {
bigEnough.add(option);
}
}
// Pick the smallest of those, assuming we found any
if (bigEnough.size() > 0) {
return Collections.min(bigEnough, new CompareSizesByArea());
} else {
Log.e(TAG, "Couldn't find any suitable preview size");
return choices[0];
}
}
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_camera2_video_image);
File dir = new File(Environment.getExternalStoragePublicDirectory(
Environment.DIRECTORY_MOVIES) + File.separator + AppConstants.APPDIRRECORDING);
if (dir.isDirectory()) {
deleteDirectory(dir);
}
videoList = new ArrayList<>();
mTextureView = findViewById(R.id.textureView);
mRecordButton = findViewById(R.id.videoOnlineImageButton);
mRecordButton.setImageResource(R.drawable.ic_video);
mCheckPoint = findViewById(R.id.checkPoint);
mCheckPoint.setVisibility(View.GONE);
mDots = findViewById(R.id.dot);
mRecordButton.setOnClickListener(this);
flashButton = findViewById(R.id.flashVideo);
switchCamera = findViewById(R.id.switchVideo);
revertVideo = findViewById(R.id.revertVideo);
revertVideo.setVisibility(View.GONE);
mChronometer = findViewById(R.id.chronometer);
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
flashOpt = prefs.getString(getString(R.string.flash_option), getString(R.string.auto));
if (flashOpt.equals(getString(R.string.flash_off)))
flashButton.setImageResource(R.drawable.flash_auto);
else if (flashOpt.equals(getString(R.string.flash_on)))
flashButton.setImageResource(R.drawable.flash_on);
else
flashButton.setImageResource(R.drawable.flash_off);
findViewById(R.id.checkPoint).setOnClickListener(this);
findViewById(R.id.flashVideo).setOnClickListener(this);
findViewById(R.id.switchVideo).setOnClickListener(this);
findViewById(R.id.revertVideo).setOnClickListener(this);
}
@Override
public void onResume() {
super.onResume();
startBackgroundThread();
if (mTextureView.isAvailable()) {
openCamera(mTextureView.getWidth(), mTextureView.getHeight());
} else {
mTextureView.setSurfaceTextureListener(mSurfaceTextureListener);
}
if(mIsRecordingVideo)
mRecordButton.setImageResource(R.drawable.ic_video_stop);
else
mRecordButton.setImageResource(R.drawable.ic_video);
mCheckPoint.setEnabled(true);
startTime=SystemClock.uptimeMillis();
customHandler.postDelayed(updateTimerThread, 0);
}
@Override
public void onPause() {
closeCamera();
mCheckPoint.setEnabled(false);
timeSwapBuff += timeInMilliseconds;
customHandler.removeCallbacks(updateTimerThread);
stopBackgroundThread();
super.onPause();
}
private Runnable updateTimerThread = new Runnable() {
public void run() {
timeInMilliseconds = SystemClock.uptimeMillis() - startTime;
updatedTime = timeSwapBuff + timeInMilliseconds;
int secs = (int) (updatedTime / 1000);
int mins = secs / 60;
secs = secs % 60;
int hour = mins / 60;
mChronometer.setText("" + hour + ":"
+ String.format("%02d", mins) + ":"
+ String.format("%02d", secs));
customHandler.postDelayed(this, 0);
}
};
@Override
public void onClick(View view) {
switch (view.getId()) {
case R.id.videoOnlineImageButton: {
if (mIsRecordingVideo) {
mDots.setVisibility(View.GONE);
mChronometer.setVisibility(View.GONE);
switchCamera.setVisibility(View.VISIBLE);
mCheckPoint.setVisibility(View.GONE);
stopRecordingVideo();
Intent mediaStoreUpdateIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
mediaStoreUpdateIntent.setData(Uri.fromFile(new File(mNextVideoAbsolutePath)));
sendBroadcast(mediaStoreUpdateIntent);
} else {
mCheckPoint.setVisibility(View.VISIBLE);
switchCamera.setVisibility(View.GONE);
mChronometer.setVisibility(View.VISIBLE);
mDots.setVisibility(View.VISIBLE);
startRecordingVideo();
}
break;
}
case R.id.switchVideo: {
facingCamera = !facingCamera;
closeCamera();
if (mTextureView.isAvailable()) {
openCamera(mTextureView.getWidth(), mTextureView.getHeight());
} else {
mTextureView.setSurfaceTextureListener(mSurfaceTextureListener);
}
break;
}
case R.id.flashVideo: {
if (onFlashCheck()) {
CameraCharacteristics cameraCharacteristics = null;
try {
cameraCharacteristics = manager.getCameraCharacteristics(cameraId);
} catch (CameraAccessException e) {
e.printStackTrace();
}
Boolean available = cameraCharacteristics.get(CameraCharacteristics.FLASH_INFO_AVAILABLE);
isFlashSupported = available == null ? false : available;
switchFlash();
}
break;
}
}
}
private void startBackgroundThread() {
mBackgroundThread = new HandlerThread("CameraBackground");
mBackgroundThread.start();
mBackgroundHandler = new Handler(mBackgroundThread.getLooper());
}
private void stopBackgroundThread() {
mBackgroundThread.quitSafely();
try {
mBackgroundThread.join();
mBackgroundThread = null;
mBackgroundHandler = null;
} catch (InterruptedException e) {
e.printStackTrace();
}
}
@SuppressLint("MissingPermission")
private void openCamera(int width, int height) {
final Activity activity = this;
if (null == activity || activity.isFinishing()) {
return;
}
manager = (CameraManager) activity.getSystemService(Context.CAMERA_SERVICE);
try {
Log.d(TAG, "tryAcquire");
if (!mCameraOpenCloseLock.tryAcquire(2500, TimeUnit.MILLISECONDS)) {
throw new RuntimeException("Time out waiting to lock camera opening.");
}
cameraId = manager.getCameraIdList()[1];
if (facingCamera) {
cameraId = manager.getCameraIdList()[1];
flashButton.setVisibility(View.GONE);
} else {
cameraId = manager.getCameraIdList()[0];
flashButton.setVisibility(View.VISIBLE);
}
// Choose the sizes for camera preview and video recording
CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
StreamConfigurationMap map = characteristics
.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
mSensorOrientation = characteristics.get(CameraCharacteristics.SENSOR_ORIENTATION);
if (map == null) {
throw new RuntimeException("Cannot get available preview/video sizes");
}
mVideoSize = chooseVideoSize(map.getOutputSizes(MediaRecorder.class));
mPreviewSize = chooseOptimalSize(map.getOutputSizes(SurfaceTexture.class),
width, height, mVideoSize);
int orientation = getResources().getConfiguration().orientation;
if (orientation == Configuration.ORIENTATION_LANDSCAPE) {
mTextureView.setAspectRatio(mPreviewSize.getWidth(), mPreviewSize.getHeight());
} else {
mTextureView.setAspectRatio(mPreviewSize.getHeight(), mPreviewSize.getWidth());
}
configureTransform(width, height);
mMediaRecorder = new MediaRecorder();
manager.openCamera(cameraId, mStateCallback, null);
} catch (CameraAccessException e) {
Toast.makeText(activity, "Cannot access the camera.", Toast.LENGTH_SHORT).show();
activity.finish();
} catch (NullPointerException e) {
} catch (InterruptedException e) {
throw new RuntimeException("Interrupted while trying to lock camera opening.");
}
}
private void closeCamera() {
try {
mCameraOpenCloseLock.acquire();
closePreviewSession();
if (null != mCameraDevice) {
mCameraDevice.close();
mCameraDevice = null;
}
if (null != mMediaRecorder) {
mMediaRecorder.release();
mMediaRecorder = null;
}
} catch (InterruptedException e) {
throw new RuntimeException("Interrupted while trying to lock camera closing.");
} finally {
mCameraOpenCloseLock.release();
}
}
private void startPreview() {
if (null == mCameraDevice || !mTextureView.isAvailable() || null == mPreviewSize) {
return;
}
try {
closePreviewSession();
SurfaceTexture texture = mTextureView.getSurfaceTexture();
assert texture != null;
texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
Surface previewSurface = new Surface(texture);
mPreviewBuilder.addTarget(previewSurface);
mCameraDevice.createCaptureSession(Collections.singletonList(previewSurface),
new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(@NonNull CameraCaptureSession session) {
mPreviewSession = session;
updatePreview();
}
@Override
public void onConfigureFailed(@NonNull CameraCaptureSession session) {
Toast.makeText(RecordVideoActivity.this, "Failed", Toast.LENGTH_SHORT).show();
}
}, mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
private void updatePreview() {
if (null == mCameraDevice) {
return;
}
try {
setUpCaptureRequestBuilder(mPreviewBuilder);
HandlerThread thread = new HandlerThread("CameraPreview");
thread.start();
mPreviewSession.setRepeatingRequest(mPreviewBuilder.build(), null, mBackgroundHandler);
} catch (CameraAccessException e) {
e.printStackTrace();
}
}
private void setUpCaptureRequestBuilder(CaptureRequest.Builder builder) {
if (onFlashCheck()) {
runOnUiThread(new Runnable() {
@Override
public void run() {
flashButton.setVisibility(View.VISIBLE);
}
});
if (flashOpt.equals(getString(R.string.auto)))
builder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
else if (flashOpt.equals(getString(R.string.flash_off)))
builder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_OFF);
else
builder.set(CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_TORCH);
} else
runOnUiThread(new Runnable() {
@Override
public void run() {
flashButton.setVisibility(View.GONE);
}
});
}
private void configureTransform(int viewWidth, int viewHeight) {
if (null == mTextureView || null == mPreviewSize) {
return;
}
int rotation = getWindowManager().getDefaultDisplay().getRotation();
Matrix matrix = new Matrix();
RectF viewRect = new RectF(0, 0, viewWidth, viewHeight);
RectF bufferRect = new RectF(0, 0, mPreviewSize.getHeight(), mPreviewSize.getWidth());
float centerX = viewRect.centerX();
float centerY = viewRect.centerY();
if (Surface.ROTATION_90 == rotation || Surface.ROTATION_270 == rotation) {
bufferRect.offset(centerX - bufferRect.centerX(), centerY - bufferRect.centerY());
matrix.setRectToRect(viewRect, bufferRect, Matrix.ScaleToFit.FILL);
float scale = Math.max(
(float) viewHeight / mPreviewSize.getHeight(),
(float) viewWidth / mPreviewSize.getWidth());
matrix.postScale(scale, scale, centerX, centerY);
matrix.postRotate(90 * (rotation - 2), centerX, centerY);
}
mTextureView.setTransform(matrix);
}
private void setUpMediaRecorder() throws IOException {
mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);
mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
File file = getVideoFilePath(this);
mNextVideoAbsolutePath = file.getAbsolutePath();
videoName = file.getName();
mMediaRecorder.setOutputFile(mNextVideoAbsolutePath);
mMediaRecorder.setVideoEncodingBitRate(10000000);
mMediaRecorder.setVideoFrameRate(30);
mMediaRecorder.setVideoSize(mVideoSize.getWidth(), mVideoSize.getHeight());
mMediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.H264);
mMediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC);
int rotation = getWindowManager().getDefaultDisplay().getRotation();
switch (mSensorOrientation) {
case SENSOR_ORIENTATION_DEFAULT_DEGREES:
mMediaRecorder.setOrientationHint(DEFAULT_ORIENTATIONS.get(rotation));
break;
case SENSOR_ORIENTATION_INVERSE_DEGREES:
mMediaRecorder.setOrientationHint(INVERSE_ORIENTATIONS.get(rotation));
break;
}
mMediaRecorder.prepare();
}
private File getVideoFilePath(Context context) {
File appDir = new File(Environment.getExternalStoragePublicDirectory(
Environment.DIRECTORY_MOVIES) + File.separator + AppConstants.APPDIRRECORDING);
if (!appDir.isDirectory()) {
appDir.mkdirs();
}
String timestamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
String prepend = "VIDEO_" + timestamp + ".mp4";
File videoFile = null;
try {
videoFile = File.createTempFile(prepend, ".mp4", appDir);
} catch (IOException e) {
e.printStackTrace();
}
return videoFile;
}
private void startRecordingVideo() {
if (null == mCameraDevice || !mTextureView.isAvailable() || null == mPreviewSize) {
return;
}
try {
closePreviewSession();
setUpMediaRecorder();
SurfaceTexture texture = mTextureView.getSurfaceTexture();
assert texture != null;
texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
mPreviewBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_RECORD);
List<Surface> surfaces = new ArrayList<>();
// Set up Surface for the camera preview
Surface previewSurface = new Surface(texture);
surfaces.add(previewSurface);
mPreviewBuilder.addTarget(previewSurface);
// Set up Surface for the MediaRecorder
Surface recorderSurface = mMediaRecorder.getSurface();
surfaces.add(recorderSurface);
mPreviewBuilder.addTarget(recorderSurface);
mCameraDevice.createCaptureSession(surfaces, new CameraCaptureSession.StateCallback() {
@Override
public void onConfigured(@NonNull final CameraCaptureSession cameraCaptureSession) {
runOnUiThread(new Runnable() {
@Override
public void run() {
mPreviewSession = cameraCaptureSession;
updatePreview();
mIsRecordingVideo = true;
startTime = SystemClock.uptimeMillis();
mChronometer.setVisibility(View.VISIBLE);
customHandler.postDelayed(updateTimerThread, 0);
mRecordButton.setImageResource(R.drawable.ic_video_stop);
mMediaRecorder.start();
mCheckPoint.setEnabled(true);
}
});
}
@Override
public void onConfigureFailed(@NonNull CameraCaptureSession cameraCaptureSession) {
Toast.makeText(RecordVideoActivity.this, "Failed", Toast.LENGTH_SHORT).show();
}
}, mBackgroundHandler);
} catch (CameraAccessException | IOException e) {
e.printStackTrace();
}
}
private void closePreviewSession() {
if (mPreviewSession != null) {
mPreviewSession.close();
mPreviewSession = null;
}
}
@SuppressLint("ResourceType")
private void stopRecordingVideo() {
mIsRecordingVideo = false;
customHandler.removeCallbacks(updateTimerThread);
mRecordButton.setImageResource(R.drawable.ic_video);
if(mMediaRecorder!=null) {
try {
mMediaRecorder.stop();
} catch (RuntimeException e) {
e.printStackTrace();
}
mMediaRecorder.reset();
}
}
static class CompareSizesByArea implements Comparator<Size> {
@Override
public int compare(Size lhs, Size rhs) {
return Long.signum((long) lhs.getWidth() * lhs.getHeight() -
(long) rhs.getWidth() * rhs.getHeight());
}
}
@Override
protected void onDestroy() {
customHandler.removeCallbacks(updateTimerThread);
}
。表达式sorting将调用sorting(a, b)并返回bool。排序例程sorting会多次调用std::sort。
这个名字并不好。我建议sorting而不是排序＆＃39;。此外，参数化是错误的。它比较了学生的percent_less_than。
percent答案 1 :(得分：1)
Jive Dadson正确回答了您的问题。
您还可以使用lambda语法进行排序。
sort(container.begin(), container.end(), [=](const student_info &a, const student_info &b) {
return a.percent < b.percent;
});