qt-bugs@ issue : N84155
applied: yes
author: dfaure

Fix datastream<<qint64 code to actually write to the stream, not read from it (!), in 3-1-compat mode.

    qint64 value = 0x1234567887654321LL;
    QByteArray data;
    QDataStream arg( &data, QIODevice::WriteOnly );
    arg.setVersion( QDataStream::Qt_3_1 );
    arg << value;

Without the patch, this fails with ""QIODevice::read called on a WriteOnly device".

Index: qdatastream.cpp
===================================================================
--- src/corelib/io/qdatastream.cpp.orig	(revision 452002)
+++ src/corelib/io/qdatastream.cpp	(working copy)
@@ -985,8 +985,9 @@ QDataStream &QDataStream::operator<<(qin
 {
     CHECK_STREAM_PRECOND(*this)
     if (version() < 6) {
-        quint32 i1, i2;
-        *this >> i2 >> i1;
+        quint32 i1 = i >> 32;
+        quint32 i2 = i & 0xFFFFFFFF;
+        *this << i2 << i1;
         i = ((quint64)i1 << 32) + i2;
     } else if (noswap) {                        // no conversion needed
         dev->write((char *)&i, sizeof(qint64));