今天调试代码时遇到一个奇怪的问题，不过一般感觉比较奇怪的问题，最后查到原因时，原因都比较简单！
编译问题
先来看一下qt的编译错误，提示一堆错误:
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qglobal.h:1173:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qnamespace.h:43,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qobjectdefs.h:48,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:46,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qtypeinfo.h: In instantiation of 'class QTypeInfo<QVariant>':
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:459:31: required from 'void QList<T>::node_copy(QList<T>::Node*, QList<T>::Node*, QList<T>::Node*) [with T = QVariant]'
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:813:22: required from 'QList<T>::QList(const QList<T>&) [with T = QVariant]'
temp\moc\moc_test.cpp:103:82: required from here
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qtypeinfo.h:67:26: error: invalid application of 'sizeof' to incomplete type 'QVariant'
isLarge = (sizeof(T)>sizeof(void*)),
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qtypeinfo.h:69:24: error: invalid application of 'sizeof' to incomplete type 'QVariant'
sizeOf = sizeof(T)
^
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:49:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h: In instantiation of 'void QList<T>::node_copy(QList<T>::Node*, QList<T>::Node*, QList<T>::Node*) [with T = QVariant]':
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:813:22: required from 'QList<T>::QList(const QList<T>&) [with T = QVariant]'
temp\moc\moc_test.cpp:103:82: required from here
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:462:28: error: invalid use of incomplete type 'class QVariant'
current->v = new T(*reinterpret_cast<T*>(src->v));
^
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:54:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:114:21: note: forward declaration of 'class QVariant'
F(QVariant, 41, QVariant) \
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1924:11: note: in definition of macro 'QT_FORWARD_DECLARE_STATIC_TYPES_ITER'
class Name;
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1926:1: note: in expansion of macro 'QT_FOR_EACH_STATIC_CORE_CLASS'
QT_FOR_EACH_STATIC_CORE_CLASS(QT_FORWARD_DECLARE_STATIC_TYPES_ITER)
^
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:49:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:468:17: warning: possible problem detected in invocation of delete operator: [-Wdelete-incomplete]
delete reinterpret_cast<T*>(current->v);
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:468:17: warning: invalid use of incomplete type 'class QVariant'
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:54:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:114:21: note: forward declaration of 'class QVariant'
F(QVariant, 41, QVariant) \
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1924:11: note: in definition of macro 'QT_FORWARD_DECLARE_STATIC_TYPES_ITER'
class Name;
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1926:1: note: in expansion of macro 'QT_FOR_EACH_STATIC_CORE_CLASS'
QT_FOR_EACH_STATIC_CORE_CLASS(QT_FORWARD_DECLARE_STATIC_TYPES_ITER)
^
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:49:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:468:17: note: neither the destructor nor the class-specific operator delete will be called, even if they are declared when the class is defined
delete reinterpret_cast<T*>(current->v);
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:475:17: error: invalid use of incomplete type 'class QVariant'
new (current) T(*reinterpret_cast<T*>(src));
^
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:54:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:114:21: note: forward declaration of 'class QVariant'
F(QVariant, 41, QVariant) \
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1924:11: note: in definition of macro 'QT_FORWARD_DECLARE_STATIC_TYPES_ITER'
class Name;
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1926:1: note: in expansion of macro 'QT_FOR_EACH_STATIC_CORE_CLASS'
QT_FOR_EACH_STATIC_CORE_CLASS(QT_FORWARD_DECLARE_STATIC_TYPES_ITER)
^
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:49:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:481:17: error: invalid use of incomplete type 'class QVariant'
(reinterpret_cast<T*>(current))->~T();
^
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:54:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:114:21: note: forward declaration of 'class QVariant'
F(QVariant, 41, QVariant) \
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1924:11: note: in definition of macro 'QT_FORWARD_DECLARE_STATIC_TYPES_ITER'
class Name;
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1926:1: note: in expansion of macro 'QT_FOR_EACH_STATIC_CORE_CLASS'
QT_FOR_EACH_STATIC_CORE_CLASS(QT_FORWARD_DECLARE_STATIC_TYPES_ITER)
^
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:49:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h: In instantiation of 'void QList<T>::node_destruct(QList<T>::Node*, QList<T>::Node*) [with T = QVariant]':
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:865:18: required from 'void QList<T>::dealloc(QListData::Data*) [with T = QVariant]'
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:827:16: required from 'QList<T>::~QList() [with T = QVariant]'
temp\moc\moc_test.cpp:103:82: required from here
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:494:31: warning: possible problem detected in invocation of delete operator: [-Wdelete-incomplete]
while(from != to) --to, delete reinterpret_cast<T*>(to->v);
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:494:31: warning: invalid use of incomplete type 'class QVariant'
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:54:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:114:21: note: forward declaration of 'class QVariant'
F(QVariant, 41, QVariant) \
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1924:11: note: in definition of macro 'QT_FORWARD_DECLARE_STATIC_TYPES_ITER'
class Name;
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1926:1: note: in expansion of macro 'QT_FOR_EACH_STATIC_CORE_CLASS'
QT_FOR_EACH_STATIC_CORE_CLASS(QT_FORWARD_DECLARE_STATIC_TYPES_ITER)
^
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:49:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:494:31: note: neither the destructor nor the class-specific operator delete will be called, even if they are declared when the class is defined
while(from != to) --to, delete reinterpret_cast<T*>(to->v);
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qlist.h:496:32: error: invalid use of incomplete type 'class QVariant'
while (from != to) --to, reinterpret_cast<T*>(to)->~T();
^
In file included from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/qobject.h:54:0,
from D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include\QtCore/QObject:1,
from temp\moc\../../../test/module_function/test.h:4,
from temp\moc\moc_test.cpp:9:
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:114:21: note: forward declaration of 'class QVariant'
F(QVariant, 41, QVariant) \
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1924:11: note: in definition of macro 'QT_FORWARD_DECLARE_STATIC_TYPES_ITER'
class Name;
^
D:\Qt\Qt5.10.0\5.10.0\mingw53_32\include/QtCore/qmetatype.h:1926:1: note: in expansion of macro 'QT_FOR_EACH_STATIC_CORE_CLASS'
QT_FOR_EACH_STATIC_CORE_CLASS(QT_FORWARD_DECLARE_STATIC_TYPES_ITER)
^
Makefile.Debug:3709: recipe for target 'temp/obj/moc_test.o' failed
mingw32-make[1]: Leaving directory 'E:/code/test-Debug'
Makefile:36: recipe for target 'debug' failed
mingw32-make[1]: *** [temp/obj/moc_test.o] Error 1
mingw32-make: *** [debug] Error 2
18:04:40: 进程"D:\Qt\Qt5.10.0\Tools\mingw530_32\bin\mingw32-make.exe"退出，退出代码 2 。
Error while building/deploying project test (kit: Desktop Qt 5.10.0 MinGW 32bit)
When executing step "Make"排查问题
从这里面可以看出，基本上是与QVariant类型的使用有关系，查了下代码，里面没有直接使用QVariant类型的地方，到是有一个信号的参数类型，使用的是QVariantList，怀疑有可能是这个信号引起的，把这信号注释掉之后，编译不在报错。然后类里面的成员变量里使用QVariantList定义的成员变量，则不会导致这个编译错误！
另外，通过查看编译错误，可以发现，是编译moc_test.cpp文件时开始报错的，也就是说，在编译moc文件时提示报错，moc文件里第9行是#include " temp\moc\../../../test/module_function/test.h"，引用的是测试类的头文件，也看不出什么错误。
只是尝试给test.h里加了个头文件引用：#include <QVariantList>，再次编译错误没有了，编译通过！
问题原因
使用QVariantList作为信号的参数时，一定引用头文件：
#include <QVariantList>
否则会编译错误，如果不作为信号的参数，只是作为成员变量用，或者成员函数的参数，不引用其头文件也不会报错。
这两种情况编译是有点区别的，moc文件是qt编译器根据类源文件自动生成的代码。
在此记录一下，以免以后调试遇到同样的问题而浪费时间。
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