我是使用Qt Creator 2.8.1（Qt 5.1.1）开发的新手。为了实现基于 ftp 的应用程序，我搜索并发现要使用 QFtp 才能将其安装在当前的 Qt 版本中。所以我从 https://qt.gitorious.org/qt/qtftp/下载了它。
在安装过程中，我遇到了以下问题，但到目前为止还没有找到任何解决方案。它总是说"错误：在这种情况下"：
leo@ubuntu:~$ cd Desktop/
leo@ubuntu:~/Desktop$ cd qt-qtftp/
leo@ubuntu:~/Desktop/qt-qtftp$ qmake
leo@ubuntu:~/Desktop/qt-qtftp$ make
cd src/ && make -f Makefile
make[1]: Entering directory `/home/leo/Desktop/qt-qtftp/src'
cd qftp/ && make -f Makefile
make[2]: Entering directory `/home/leo/Desktop/qt-qtftp/src/qftp'
g++ -c -pipe -O2 -Wall -W -D_REENTRANT -DQT_WEBKIT -DQT_NO_DEBUG -DQT_NETWORK_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtNetwork -I/usr/include/qt4 -I. -o qftp.o qftp.cpp
In file included from qftp.cpp:45:0:
qftp.h: In member function ‘void QFtpPrivate::_q_startNextCommand()’:
qftp.h:144:10: error: ‘void QFtp::commandStarted(int)’ is protected
qftp.cpp:2201:33: error: within this context
In file included from qftp.cpp:45:0:
qftp.h:138:10: error: ‘void QFtp::stateChanged(int)’ is protected
qftp.cpp:2254:39: error: within this context
In file included from qftp.cpp:45:0:
qftp.h: In member function ‘void QFtpPrivate::_q_piFinished(const QString&)’:
qftp.h:145:10: error: ‘void QFtp::commandFinished(int, bool)’ is protected
qftp.cpp:2278:48: error: within this context
In file included from qftp.cpp:45:0:
qftp.h:146:10: error: ‘void QFtp::done(bool)’ is protected
qftp.cpp:2284:34: error: within this context
In file included from qftp.cpp:45:0:
qftp.h: In member function ‘void QFtpPrivate::_q_piError(int, const QString&)’:
qftp.h:145:10: error: ‘void QFtp::commandFinished(int, bool)’ is protected
qftp.cpp:2356:40: error: within this context
In file included from qftp.cpp:45:0:
qftp.h:146:10: error: ‘void QFtp::done(bool)’ is protected
qftp.cpp:2361:26: error: within this context
In file included from qftp.cpp:45:0:
qftp.h: In member function ‘void QFtpPrivate::_q_piConnectState(int)’:
qftp.h:138:10: error: ‘void QFtp::stateChanged(int)’ is protected
qftp.cpp:2371:38: error: within this context
In file included from qftp.cpp:45:0:
qftp.h: In member function ‘void QFtpPrivate::_q_piFtpReply(int, const QString&)’:
qftp.h:142:10: error: ‘void QFtp::rawCommandReply(int, const QString&)’ is protected
qftp.cpp:2384:50: error: within this context
make[2]: *** [qftp.o] Error 1
make[2]: Leaving directory `/home/leo/Desktop/qt-qtftp/src/qftp'
make[1]: *** [sub-qftp-make_default] Error 2
make[1]: Leaving directory `/home/leo/Desktop/qt-qtftp/src'
make: *** [sub-src-make_default] Error 2
您是针对 Qt 4 构建的，但此代码显然只是 Qt 5，并且依赖于 Qt 5 中公开的信号（它们在 Qt 4 中受到保护）。
查看为 g++ 设置的包含路径：
g++ -c [...] -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtNetwork -I/usr/include/qt4 -I. -o qftp.o qftp.cpp
使用系统范围安装的Qt 4。
我认为这是一个意外，你只需要在Qt Creator中选择正确的Qt版本（Qt 5.1.1）。