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c++ - 将一个文件分成几个部分

转载 作者:太空宇宙 更新时间:2023-11-04 13:53:24 25 4
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我正在尝试在 Qt 中制作一个文件复制应用程序。我需要将源文件拆分成几个文件,以便我的复制函数可以一个接一个地复制部分数据并更新 QProgressBar。为了准确更新进度,我需要将源文件拆分为原始大小的 1%。我的方法是不是错了。我找不到关于此主题的大量资源。如何将源文件拆分为大小相等的几个部分?

最佳答案

以下是这种异步文件复制器的独立草图。有一些不足:

  1. 报错也需要报出QFile错误码。

  2. 处理互斥 RAII 确实需要自定义互斥锁类。

查看代码时,请确保分别考虑实现和接口(interface)(其使用)。该界面使其易于使用。实现的相对复杂性使得易于使用的界面成为可能。

#include <QApplication>
#include <QByteArray>
#include <QProgressDialog>
#include <QFileDialog>
#include <QBasicTimer>
#include <QElapsedTimer>
#include <QThread>
#include <QMutex>
#include <QFile>
#include <limits>

class FileCopier : public QObject {
Q_OBJECT
QMutex mutable m_mutex;
QByteArray m_buf;
QBasicTimer m_copy, m_progress;
QString m_error;
QFile m_fi, m_fo;
qint64 m_total, m_done;
int m_shift;

void close() {
m_copy.stop();
m_progress.stop();
m_fi.close();
m_fo.close();
m_mutex.unlock();
}
/// Takes the error string from given file and emits an error indication.
/// Closes the files and stops the copy. Always returns false
bool error(QFile & f) {
m_error = f.errorString();
m_error.append(QStringLiteral("(in %1 file").arg(f.objectName()));
emit finished(false, m_error);
close();
return false;
}
void finished() {
emitProgress();
emit finished(m_done == m_total, m_error);
close();
}
void emitProgress() {
emit progressed(m_done, m_total);
emit hasProgressValue(m_done >> m_shift);
}
void timerEvent(QTimerEvent * ev) {
if (ev->timerId() == m_copy.timerId()) {
// Do the copy
qint64 read = m_fi.read(m_buf.data(), m_buf.size());
if (read == -1) { error(m_fi); return; }
if (read == 0) return finished();
qint64 written = m_fo.write(m_buf.constData(), read);
if (written == -1) { error(m_fo); return; }
Q_ASSERT(written == read);
m_done += read;
}
else if (ev->timerId() == m_progress.timerId())
emitProgress();
}
Q_INVOKABLE void cancelImpl() {
if (!m_fi.isOpen()) return;
m_error = "Canceled";
finished();
}
public:
explicit FileCopier(QObject * parent = 0) :
QObject(parent),
// Copy 64kbytes at a time. On a modern hard drive, we'll copy
// on the order of 1000 such blocks per second.
m_buf(65536, Qt::Uninitialized)
{
m_fi.setObjectName("source");
m_fo.setObjectName("destination");
}
/// Copies a file to another with progress indication.
/// Returns false if the files cannot be opened.
/// This method is thread safe.
Q_SLOT bool copy(const QString & src, const QString & dst) {
bool locked = m_mutex.tryLock();
Q_ASSERT_X(locked, "copy",
"Another copy is already in progress");
m_error.clear();

// Open the files
m_fi.setFileName(src);
m_fo.setFileName(dst);
if (! m_fi.open(QIODevice::ReadOnly)) return error(m_fi);
if (! m_fo.open(QIODevice::WriteOnly)) return error(m_fo);
m_total = m_fi.size();
if (m_total < 0) return error(m_fi);

// File size might not fit into an integer, calculate the number of
// binary digits to shift it right by. Recall that QProgressBar etc.
// all use int, not qint64!
m_shift = 0;
while ((m_total>>m_shift) >= std::numeric_limits<int>::max()) m_shift++;
emit hasProgressMaximum(m_total>>m_shift);

m_done = 0;
m_copy.start(0, this);
m_progress.start(100, this); // Progress is emitted at 10Hz rate
return true;
}
/// This method is thread safe only when a copy is not in progress.
QString lastError() const {
bool locked = m_mutex.tryLock();
Q_ASSERT_X(locked, "lastError",
"A copy is in progress. This method can only be used when"
"a copy is done");
QString error = m_error;
m_mutex.unlock();
return error;
}
/// Cancels a pending copy operation. No-op if no copy is underway.
/// This method is thread safe.
Q_SLOT void cancel() {
QMetaObject::invokeMethod(this, "cancelImpl");
}
/// Signal for progress indication with number of bytes
Q_SIGNAL void progressed(qint64 done, qint64 total);
/// Signals for progress that uses abstract integer values
Q_SIGNAL void hasProgressMaximum(int total);
Q_SIGNAL void hasProgressValue(int done);
///
Q_SIGNAL void finished(bool ok, const QString & error);
};

/// A thread that is always destructible: if quits the event loop and waits
/// for it to finish.
class Thread : public QThread {
public:
~Thread() { quit(); wait(); }
};

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QString src = QFileDialog::getOpenFileName(0, "Source File");
if (src.isEmpty()) return 1;
QString dst = QFileDialog::getSaveFileName(0, "Destination File");
if (dst.isEmpty()) return 1;

QProgressDialog dlg("File Copy Progress", "Cancel", 0, 100);
Q_ASSERT(!dlg.isModal());
Thread thread;
FileCopier copier;
copier.moveToThread(&thread);
thread.start();
dlg.connect(&copier, SIGNAL(hasProgressMaximum(int)),
SLOT(setMaximum(int)));
dlg.connect(&copier, SIGNAL(hasProgressValue(int)),
SLOT(setValue(int)));
copier.connect(&dlg, SIGNAL(canceled()), SLOT(cancel()));
a.connect(&copier, SIGNAL(finished(bool,QString)), SLOT(quit()));
// The copy method is thread safe.
copier.copy(src, dst);
return a.exec();
}

#include "main.moc"

关于c++ - 将一个文件分成几个部分,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/22587752/

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