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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