得到一堆十字架初始化错误 [英] Getting a bunch of crosses initialization error
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问题描述
我从下载的示例中截取了这段代码:
I have this snippets of code taken from a downloaded example:
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:
Now if compile the program I get this errors:
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 case 语句的括号，我会收到此错误:
Now if removed the brackets of case statment I get this error:
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("
"))
{
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) 我是不是用错了方括号?
1) Am I using brackets incorrectly?
2) 为什么在 case 语句中使用方括号会显示 crosses initialization 到其他代码行.
2) Why using brackets in case statement shows crosses initialization to other lines of code.
推荐答案
C++ 标准说:
可以转移到一个块中，但不能以某种方式转移通过初始化绕过声明.一个程序从一个具有自动存储持续时间的局部变量不在的点范围到它在范围内的点是格式错误的，除非变量具有 POD 类型 (3.9) 并且在没有初始化程序的情况下声明.
It is possible to transfer into a block, but not in a way that bypasses declarations with initialization. A program that jumps from a point where a local variable with automatic storage duration is not in scope to a point where it is in scope is ill-formed unless the variable has POD type (3.9) and is declared without an initializer.
switch中的case被认为是跳转".
The cases in switch are considered as a "jump".
只需将所有对象和变量初始化在您的切换之前，一切都会好起来的.
Just put all objects and variables initializations before your switch, and everything will be fine.
考虑这段代码:
switch(k)
{
case 1:
int t = 4;
break;
default:
break;
}
这将导致交叉初始化"错误，因为可以跳过 t 的初始化，但之后它仍然在范围内，即使它从未在第一次创建地点.
It will cause a "crosses initialization" error, because it is possible to skip the initialization of t, but after that it will still be in scope, even though it was never created in the first place.
现在考虑一下:
switch(k)
{
case 1:
{
int t = 4;
}
break;
default:
break;
}
在这里，你会 not 有错误，因为变量在一个块内，并且会在块的末尾(在结束 { 处)死亡，所以在那之后它不会在任何情况下在范围内.
Here, you will not have the error, because the variable is inside a block, and will die at the end of the block ( at the closing { ), so after that it will not be in scope in any case.
要解决第一种情况，您只需要这样做:
To fix the first case, you just need to do:
int t = 0;
switch(k)
{
case 1:
t = 4;
break;
default:
break;
}
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