src_corelib_io_qdatastream.cpp

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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
#include <QFile>
 
void wrapInFunction()
{
    {
        //! [0]
        QFile file("file.dat");
        file.open(QIODevice::WriteOnly);
        QDataStream out(&file);   // we will serialize the data into the file
        out << QString("the answer is");   // serialize a string
        out << (qint32)42;        // serialize an integer
        //! [0]
    }
 
    {
        //! [1]
        QFile file("file.dat");
        file.open(QIODevice::ReadOnly);
        QDataStream in(&file);    // read the data serialized from the file
        QString str;
        qint32 a;
        in >> str >> a;           // extract "the answer is" and 42
        //! [1]
    }
 
    {
        QDataStream stream;
        //! [2]
        stream.setVersion(QDataStream::Qt_4_0);
        //! [2]
    }
 
    {
        int lots_of_interesting_data = 0;
        //! [3]
        QFile file("file.xxx");
        file.open(QIODevice::WriteOnly);
        QDataStream out(&file);
 
        // Write a header with a "magic number" and a version
        out << (quint32)0xA0B0C0D0;
        out << (qint32)123;
 
        out.setVersion(QDataStream::Qt_4_0);
 
        // Write the data
        out << lots_of_interesting_data;
        //! [3]
    }
}
 
int read_data_example()
{
    int lots_of_interesting_data = 0;
    int data_new_in_XXX_version_1_2 = 0;
    int other_interesting_data = 0;
    int XXX_BAD_FILE_FORMAT = -1;
    int XXX_BAD_FILE_TOO_OLD = -2;
    int XXX_BAD_FILE_TOO_NEW = -3;
 
    //! [4]
    QFile file("file.xxx");
    file.open(QIODevice::ReadOnly);
    QDataStream in(&file);
 
    // Read and check the header
    quint32 magic;
    in >> magic;
    if (magic != 0xA0B0C0D0)
        return XXX_BAD_FILE_FORMAT;
 
    // Read the version
    qint32 version;
    in >> version;
    if (version < 100)
        return XXX_BAD_FILE_TOO_OLD;
    if (version > 123)
        return XXX_BAD_FILE_TOO_NEW;
 
    if (version <= 110)
        in.setVersion(QDataStream::Qt_3_1);
    else
        in.setVersion(QDataStream::Qt_4_0);
 
    // Read the data
    in >> lots_of_interesting_data;
    if (version >= 120)
        in >> data_new_in_XXX_version_1_2;
    in >> other_interesting_data;
    //! [4]
 
    return 0;
}
void read_data_transaction_example(QFile file, QDataStream in)
{
    //! [5]
    QDataStream out(&file);
    out.setVersion(QDataStream::Qt_4_0);
    //! [5]
 
    //! [6]
    in.startTransaction();
    QString str;
    qint32 a;
    in >> str >> a; // try to read packet atomically
 
    if (!in.commitTransaction())
        return;     // wait for more data
    //! [6]
}