获得一堆十字架初始化错误
我从下载的例子中得到这段代码：
bool ChatServer::event(QEvent * event) { if(event->type() == QEvent::User) { UserEvent * ue = static_cast<UserEvent *>(event); switch(ue->userType) { case CR::ErrorEvent: case CR::LogEvent: { TraceEvent * te = static_cast<TraceEvent *>(ue); if(te->userType == CR::ErrorEvent) { error(te->msg); } else { log(te->msg); } } break; default: return false; } } else { return QTcpServer::event(event); } return true; } 现在如果编译程序，我得到这个错误：
g++ -c -pipe -O2 -Wall -W -DQT_NO_DEBUG -DQT_NETWORK_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/local/share/qt4/mkspecs/freebsd-g++ -I. -I/usr/local/include/qt4/QtCore -I/usr/local/include/qt4/QtNetwork -I/usr/local/include/qt4 -I. -I/usr/local/include/qt4 -I/usr/local/include -o chatserver.o chatserver.cpp g++ -c -pipe -O2 -Wall -W -DQT_NO_DEBUG -DQT_NETWORK_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/local/share/qt4/mkspecs/freebsd-g++ -I. -I/usr/local/include/qt4/QtCore -I/usr/local/include/qt4/QtNetwork -I/usr/local/include/qt4 -I. -I/usr/local/include/qt4 -I/usr/local/include -o clientservice.o clientservice.cpp clientservice.cpp: In member function 'virtual bool ClientService::event(QEvent*)': clientservice.cpp:37: error: jump to case label clientservice.cpp:34: error: crosses initialization of 'MessageEvent* me' clientservice.cpp:41: error: jump to case label clientservice.cpp:38: error: crosses initialization of 'UserInfoEvent* uie' clientservice.cpp:34: error: crosses initialization of 'MessageEvent* me' clientservice.cpp:44: error: jump to case label clientservice.cpp:38: error: crosses initialization of 'UserInfoEvent* uie' clientservice.cpp:34: error: crosses initialization of 'MessageEvent* me' clientservice.cpp:31: warning: enumeration value 'EventTypeBegin' not handled in switch clientservice.cpp:31: warning: enumeration value 'LogEvent' not handled in switch clientservice.cpp:31: warning: enumeration value 'ErrorEvent' not handled in switch clientservice.cpp:31: warning: enumeration value 'ClientConnected' not handled in switch clientservice.cpp:31: warning: enumeration value 'ClientReg' not handled in switch clientservice.cpp:31: warning: enumeration value 'ClientDisconnect' not handled in switch clientservice.cpp:31: warning: enumeration value 'ServerConnected' not handled in switch clientservice.cpp:31: warning: enumeration value 'ServerDisconnect' not handled in switch clientservice.cpp:31: warning: enumeration value 'DoConnect' not handled in switch clientservice.cpp:31: warning: enumeration value 'DoDisconnect' not handled in switch clientservice.cpp:31: warning: enumeration value 'GotMessage' not handled in switch clientservice.cpp:31: warning: enumeration value 'GotUserInfo' not handled in switch clientservice.cpp:31: warning: enumeration value 'SendUserInfo' not handled in switch clientservice.cpp:31: warning: enumeration value 'GotClientInfo' not handled in switch clientservice.cpp:31: warning: enumeration value 'SendClientInfo' not handled in switch clientservice.cpp:31: warning: enumeration value 'EventTypeEnd' not handled in switch clientservice.cpp: In member function 'void ClientService::readClient()': clientservice.cpp:63: warning: comparison between signed and unsigned integer expressions clientservice.cpp:87: error: jump to case label clientservice.cpp:83: error: crosses initialization of 'Message* msg' clientservice.cpp:92: error: jump to case label clientservice.cpp:88: error: crosses initialization of 'UserInfo* ui' clientservice.cpp:83: error: crosses initialization of 'Message* msg' clientservice.cpp:97: error: jump to case label clientservice.cpp:93: error: crosses initialization of 'ClientInfo* ci' clientservice.cpp:88: error: crosses initialization of 'UserInfo* ui' clientservice.cpp:83: error: crosses initialization of 'Message* msg' clientservice.cpp: In member function 'bool ClientService::sendToClient(CR::MsgType::MsgType, SendAble*)': clientservice.cpp:124: warning: comparison of unsigned expression < 0 is always false clientservice.cpp: In member function 'void ClientService::gotUserInfo(UserInfo*)': clientservice.cpp:176: error: cast from 'ClientService*' to 'quint32' loses precision *** Error code 1 Stop in ~/SimpleChatRoomServer
现在，如果删除的case我得到这个错误的括号：
g++ -c -pipe -O2 -Wall -W -DQT_NO_DEBUG -DQT_NETWORK_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/local/share/qt4/mkspecs/freebsd-g++ -I. -I/usr/local/include/qt4/QtCore -I/usr/local/include/qt4/QtNetwork -I/usr/local/include/qt4 -I. -I/usr/local/include/qt4 -I/usr/local/include -o chatserver.o chatserver.cpp chatserver.cpp: In member function 'virtual bool ChatServer::event(QEvent*)': chatserver.cpp:108: error: jump to case label chatserver.cpp:98: error: crosses initialization of 'TraceEvent* te' chatserver.cpp:94: warning: enumeration value 'EventTypeBegin' not handled in switch chatserver.cpp:94: warning: enumeration value 'ClientConnected' not handled in switch chatserver.cpp:94: warning: enumeration value 'ClientReg' not handled in switch chatserver.cpp:94: warning: enumeration value 'ClientDisconnect' not handled in switch chatserver.cpp:94: warning: enumeration value 'ServerConnected' not handled in switch chatserver.cpp:94: warning: enumeration value 'ServerDisconnect' not handled in switch chatserver.cpp:94: warning: enumeration value 'DoConnect' not handled in switch chatserver.cpp:94: warning: enumeration value 'DoDisconnect' not handled in switch chatserver.cpp:94: warning: enumeration value 'GotMessage' not handled in switch chatserver.cpp:94: warning: enumeration value 'SendMessage' not handled in switch chatserver.cpp:94: warning: enumeration value 'GotUserInfo' not handled in switch chatserver.cpp:94: warning: enumeration value 'SendUserInfo' not handled in switch chatserver.cpp:94: warning: enumeration value 'GotClientInfo' not handled in switch chatserver.cpp:94: warning: enumeration value 'SendClientInfo' not handled in switch chatserver.cpp:94: warning: enumeration value 'EventTypeEnd' not handled in switch *** Error code 1 Stop in ~/SimpleChatRoomServer.
SimpleChatRoomServer.cpp的完整源代码：
#include <QTextStream> #include <QDateTime> #include "traceevent.h" #include "chatserver.h" #include "chatcenterthread.h" #include "clientservicethread.h" #include "message.h" #include "server.h" ChatServer::ChatServer(QObject * parent) :QTcpServer(parent) { QFile * inFile = new QFile(this); QFile * outFile = new QFile(this); QFile * errFile = new QFile(this); inFile->open(stdin,QIODevice::ReadOnly); outFile->open(stdout,QIODevice::WriteOnly); errFile->open(stderr,QIODevice::WriteOnly); setIO(inFile,outFile,errFile); qobject_cast<Server *>(qApp)->csrId = this; csrId = (QObject *)(0+CR::ServerId); } ChatServer::~ChatServer() { for(int i = 0; i < ccs.size(); i++) { ccs.at(i)->deleteLater(); } } void ChatServer::setIO(QFile * inFile,QFile * outFile,QFile * errFile) { in.setDevice(inFile); out.setDevice(outFile); err.setDevice(errFile); } void ChatServer::incomingConnection(int socketId) { ClientServiceThread *cst = new ClientServiceThread(socketId,this); cst->start(); connect(cst,SIGNAL(finished()),cst,SLOT(deleteLater())); } bool ChatServer::init(quint16 & port) { if(!port) { bool ok = false; while(!ok) { out<<tr("Port[5555]: "); out.flush(); QString p; p = in.read(1); if(p!=QString("\n")) { QString strport; strport = in.readLine(10); strport = p + strport; port = strport.toUInt(&ok); } else { port = 5555; ok = true; } } } //ADD ONE ChatCenter ChatCenterThread * cct = new ChatCenterThread(this); cct->start(); connect(cct,SIGNAL(finished()),cct,SLOT(deleteLater())); if(!listen(QHostAddress::Any,port)) { error(tr("Listen at [%1] fail!").arg(port)); deleteLater(); exit(1); return false; } log(tr("Listen at [%1]").arg(port)); return true; } bool ChatServer::event(QEvent * event) { if(event->type() == QEvent::User) { UserEvent * ue = static_cast<UserEvent *>(event); switch(ue->userType) { case CR::ErrorEvent: case CR::LogEvent: TraceEvent * te = static_cast<TraceEvent *>(ue); if(te->userType == CR::ErrorEvent) { error(te->msg); } else { log(te->msg); } break; default: return false; } } else { return QTcpServer::event(event); } return true; } void ChatServer::error(QString msg) { err<<QDateTime::currentDateTime().toString(Qt::ISODate) <<" !ERROR! "<<msg<<endl; } void ChatServer::log(QString msg) { out<<QDateTime::currentDateTime().toString(Qt::ISODate) <<" "<<msg<<endl; }
1）我不正确地使用括号吗？
2）为什么在case语句中使用括号表示crosses initialization到其他代码行。
C ++标准说：
可以将其转换为块，但不能以绕过具有初始化的声明的方式。 从具有自动存储持续时间的局部variables不在范围内的点跳转到在范围内的点跳转的程序是不合格的，除非variables具有PODtypes（3.9），并且在没有初始化程序的情况下声明。
switch中的情况被认为是“跳跃”。
只要把所有的对象和variables初始化在你的开关之前，一切都会好的。
考虑这个代码：
switch(k) { case 1: int t = 4; break; default: break; }
它会导致一个“十字架初始化”的错误，因为它可能会跳过t的初始化，但之后它仍然在范围内 ，即使它从来没有创build。
现在考虑一下：
switch(k) { case 1: { int t = 4; } break; default: break; }
在这里，你不会有错误，因为这个variables是在一个块内部的，并且会在块的末尾（在closing { ）处死掉，所以在这之后它将不会在范围内。
要解决第一种情况，你只需要做：
int t = 0; switch(k) { case 1: t = 4; break; default: break; }
我将一些旧的代码从C移植到C ++，还有很多goto（到错误出口）。 这个问题也出现在switch语句之外。
我简单的解决gcc / g ++（用arm-linux-androideabi-gcc v4.6testing）：
如果你有
goto err_exit; int a = 1;
它抱怨。
为您的命令行添加-fmissmissive，并replace：
goto err_exit; int a; a = 1;
没什么好抱怨的。
