QSet：qHash和自定义类出错

我想创建一个QSet<Tag>，我想在程序中使用它。 Tag是我的自定义类。QSet：qHash和自定义类出错

当我建立我的代码获得关于qHash超载gcc的错误：

Exercise.cpp.o 
In file included from /opt/Qt/5.5/gcc_64/include/QtCore/qglobal.h:74:0, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/qchar.h:37, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/qstring.h:41, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/QString:1, 
       from /src/wmathtest/LaTeXText.h:4, 
       from /src/wmathtest/Exercise.h:4, 
       from /src/wmathtest/Exercise.cpp:1: 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h: In instantiation of ‘uint qHash(const T&, uint) [with T = WMathTest::Tag; uint = unsigned int]’: 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:952:32: required from ‘QHash<Key, T>::Node** QHash<Key, T>::findNode(const Key&, uint*) const [with Key = WMathTest::Tag; T = QHashDummyValue; QHash<Key, T>::Node = QHashNode<WMathTest::Tag, QHashDummyValue>; uint = unsigned int]’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:808:36: required from ‘QHash<Key, T>::iterator QHash<Key, T>::insert(const Key&, const T&) [with Key = WMathTest::Tag; T = QHashDummyValue]’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qset.h:188:94: required from ‘QSet<T>::iterator QSet<T>::insert(const T&) [with T = WMathTest::Tag]’ 
/src/wmathtest/Exercise.cpp:22:22: required from here 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:103:5: error: no matching function for call to ‘qHash(const WMathTest::Tag&)’ 
    Q_DECL_NOEXCEPT_EXPR(noexcept(qHash(t))) 
    ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:103:5: note: candidates are: 
In file included from /opt/Qt/5.5/gcc_64/include/QtCore/qset.h:37:0, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/QSet:1, 
       from /src/wmathtest/Tag.h:5, 
       from /src/wmathtest/Exercise.h:5, 
       from /src/wmathtest/Exercise.cpp:1: 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:65:52: note: constexpr uint qHash(char, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(char key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:65:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘char’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:66:52: note: constexpr uint qHash(uchar, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(uchar key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:66:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘uchar {aka unsigned char}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:67:52: note: constexpr uint qHash(signed char, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(signed char key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:67:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘signed char’ 
In file included from /opt/Qt/5.5/gcc_64/include/QtCore/qset.h:37:0, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/QSet:1, 
       from /src/wmathtest/Tag.h:5, 
       from /src/wmathtest/Exercise.h:5, 
       from /src/wmathtest/Exercise.cpp:1: 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:68:52: note: constexpr uint qHash(ushort, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(ushort key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:68:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘ushort {aka short unsigned int}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:69:52: note: constexpr uint qHash(short int, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(short key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:69:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘short int’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:70:52: note: constexpr uint qHash(uint, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(uint key, uint seed = 0) Q_DECL_NOTHROW { return key^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:70:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘uint {aka unsigned int}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:71:52: note: constexpr uint qHash(int, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(int key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:71:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘int’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:72:52: note: constexpr uint qHash(ulong, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(ulong key, uint seed = 0) Q_DECL_NOTHROW 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:72:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘ulong {aka long unsigned int}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:78:52: note: constexpr uint qHash(long int, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(long key, uint seed = 0) Q_DECL_NOTHROW { return qHash(ulong(key), seed); } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:78:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘long int’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:79:52: note: constexpr uint qHash(quint64, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(quint64 key, uint seed = 0) Q_DECL_NOTHROW 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:79:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘quint64 {aka long long unsigned int}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:83:52: note: constexpr uint qHash(qint64, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(qint64 key, uint seed = 0) Q_DECL_NOTHROW { return qHash(quint64(key), seed); } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:83:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘qint64 {aka long long int}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:84:42: note: uint qHash(float, uint) 
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION uint qHash(float key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:84:42: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘float’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:85:42: note: uint qHash(double, uint) 
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION uint qHash(double key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:85:42: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘double’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:87:42: note: uint qHash(long double, uint) 
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION uint qHash(long double key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:87:42: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘long double’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:89:52: note: constexpr uint qHash(QChar, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(const QChar key, uint seed = 0) Q_DECL_NOTHROW { return qHash(key.unicode(), seed); } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:89:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘QChar’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:90:41: note: uint qHash(const QByteArray&, uint) 
Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(const QByteArray &key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:90:41: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘const QByteArray&’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:91:41: note: uint qHash(const QString&, uint) 
Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(const QString &key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:91:41: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘const QString&’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:92:41: note: uint qHash(const QStringRef&, uint) 
Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(const QStringRef &key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:92:41: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘const QStringRef&’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:93:41: note: uint qHash(const QBitArray&, uint) 
Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(const QBitArray &key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:93:41: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘const QBitArray&’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:94:41: note: uint qHash(QLatin1String, uint) 
Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(QLatin1String key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:94:41: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘QLatin1String’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:98:32: note: template<class T> uint qHash(const T*, uint) 
template <class T> inline uint qHash(const T *key, uint seed = 0) Q_DECL_NOTHROW 
           ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:98:32: note: template argument deduction/substitution failed: 
In file included from /opt/Qt/5.5/gcc_64/include/QtCore/qglobal.h:74:0, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/qchar.h:37, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/qstring.h:41, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/QString:1, 
       from /src/wmathtest/LaTeXText.h:4, 
       from /src/wmathtest/Exercise.h:4, 
       from /src/wmathtest/Exercise.cpp:1: 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:103:5: note: mismatched types ‘const T*’ and ‘WMathTest::Tag’ 
    Q_DECL_NOEXCEPT_EXPR(noexcept(qHash(t))) 
    ^
src/wmathtest/CMakeFiles/wmathtest.dir/build.make:146: recipe for target 'src/wmathtest/CMakeFiles/wmathtest.dir/Exercise.cpp.o' failed 
make[2]: *** [src/wmathtest/CMakeFiles/wmathtest.dir/Exercise.cpp.o] Error 1 
CMakeFiles/Makefile2:160: recipe for target 'src/wmathtest/CMakeFiles/wmathtest.dir/all' failed 
make[1]: *** [src/wmathtest/CMakeFiles/wmathtest.dir/all] Error 2 
Makefile:76: recipe for target 'all' failed 
    Exercise.cpp.o 
In file included from /opt/Qt/5.5/gcc_64/include/QtCore/qglobal.h:74:0, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/qchar.h:37, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/qstring.h:41, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/QString:1, 
       from /wmathtest/LaTeXText.h:4, 
       from /src/wmathtest/Exercise.h:4, 
       from /wmathtest/Exercise.cpp:1: 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h: In instantiation of ‘uint qHash(const T&, uint) [with T = WMathTest::Tag; uint = unsigned int]’: 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:952:32: required from ‘QHash<Key, T>::Node** QHash<Key, T>::findNode(const Key&, uint*) const [with Key = WMathTest::Tag; T = QHashDummyValue; QHash<Key, T>::Node = QHashNode<WMathTest::Tag, QHashDummyValue>; uint = unsigned int]’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:808:36: required from ‘QHash<Key, T>::iterator QHash<Key, T>::insert(const Key&, const T&) [with Key = WMathTest::Tag; T = QHashDummyValue]’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qset.h:188:94: required from ‘QSet<T>::iterator QSet<T>::insert(const T&) [with T = WMathTest::Tag]’ 
/wmathtest/Exercise.cpp:22:22: required from here 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:103:5: error: no matching function for call to ‘qHash(const WMathTest::Tag&)’ 
    Q_DECL_NOEXCEPT_EXPR(noexcept(qHash(t))) 
    ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:103:5: note: candidates are: 
In file included from /opt/Qt/5.5/gcc_64/include/QtCore/qset.h:37:0, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/QSet:1, 
       from /wmathtest/Tag.h:5, 
       from /wmathtest/Exercise.h:5, 
       from /wmathtest/Exercise.cpp:1: 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:65:52: note: constexpr uint qHash(char, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(char key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:65:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘char’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:66:52: note: constexpr uint qHash(uchar, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(uchar key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:66:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘uchar {aka unsigned char}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:67:52: note: constexpr uint qHash(signed char, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(signed char key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:67:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘signed char’ 
In file included from /opt/Qt/5.5/gcc_64/include/QtCore/qset.h:37:0, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/QSet:1, 
       from /home/daniele/projects/wmathtestgenerator/src/wmathtest/Tag.h:5, 
       from /Exercise.h:5, 
       from /wmathtest/Exercise.cpp:1: 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:68:52: note: constexpr uint qHash(ushort, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(ushort key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:68:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘ushort {aka short unsigned int}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:69:52: note: constexpr uint qHash(short int, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(short key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:69:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘short int’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:70:52: note: constexpr uint qHash(uint, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(uint key, uint seed = 0) Q_DECL_NOTHROW { return key^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:70:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘uint {aka unsigned int}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:71:52: note: constexpr uint qHash(int, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(int key, uint seed = 0) Q_DECL_NOTHROW { return uint(key)^seed; } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:71:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘int’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:72:52: note: constexpr uint qHash(ulong, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(ulong key, uint seed = 0) Q_DECL_NOTHROW 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:72:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘ulong {aka long unsigned int}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:78:52: note: constexpr uint qHash(long int, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(long key, uint seed = 0) Q_DECL_NOTHROW { return qHash(ulong(key), seed); } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:78:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘long int’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:79:52: note: constexpr uint qHash(quint64, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(quint64 key, uint seed = 0) Q_DECL_NOTHROW 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:79:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘quint64 {aka long long unsigned int}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:83:52: note: constexpr uint qHash(qint64, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(qint64 key, uint seed = 0) Q_DECL_NOTHROW { return qHash(quint64(key), seed); } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:83:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘qint64 {aka long long int}’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:84:42: note: uint qHash(float, uint) 
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION uint qHash(float key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:84:42: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘float’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:85:42: note: uint qHash(double, uint) 
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION uint qHash(double key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:85:42: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘double’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:87:42: note: uint qHash(long double, uint) 
Q_CORE_EXPORT Q_DECL_CONST_FUNCTION uint qHash(long double key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:87:42: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘long double’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:89:52: note: constexpr uint qHash(QChar, uint) 
Q_DECL_CONST_FUNCTION Q_DECL_CONSTEXPR inline uint qHash(const QChar key, uint seed = 0) Q_DECL_NOTHROW { return qHash(key.unicode(), seed); } 
                ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:89:52: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘QChar’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:90:41: note: uint qHash(const QByteArray&, uint) 
Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(const QByteArray &key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:90:41: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘const QByteArray&’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:91:41: note: uint qHash(const QString&, uint) 
Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(const QString &key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:91:41: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘const QString&’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:92:41: note: uint qHash(const QStringRef&, uint) 
Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(const QStringRef &key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:92:41: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘const QStringRef&’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:93:41: note: uint qHash(const QBitArray&, uint) 
Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(const QBitArray &key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:93:41: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘const QBitArray&’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:94:41: note: uint qHash(QLatin1String, uint) 
Q_CORE_EXPORT Q_DECL_PURE_FUNCTION uint qHash(QLatin1String key, uint seed = 0) Q_DECL_NOTHROW; 
             ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:94:41: note: no known conversion for argument 1 from ‘const WMathTest::Tag’ to ‘QLatin1String’ 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:98:32: note: template<class T> uint qHash(const T*, uint) 
template <class T> inline uint qHash(const T *key, uint seed = 0) Q_DECL_NOTHROW 
           ^
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:98:32: note: template argument deduction/substitution failed: 
In file included from /opt/Qt/5.5/gcc_64/include/QtCore/qglobal.h:74:0, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/qchar.h:37, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/qstring.h:41, 
       from /opt/Qt/5.5/gcc_64/include/QtCore/QString:1, 
       from /home/daniele/projects/wmathtestgenerator/src/wmathtest/LaTeXText.h:4, 
       from /home/daniele/projects/wmathtestgenerator/src/wmathtest/Exercise.h:4, 
       from /thtest/Exercise.cpp:1: 
/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:103:5: note: mismatched types ‘const T*’ and ‘WMathTest::Tag’ 
    Q_DECL_NOEXCEPT_EXPR(noexcept(qHash(t))) 
    ^
src/wmathtest/CMakeFiles/wmathtest.dir/build.make:146: recipe for target 'src/wmathtest/CMakeFiles/wmathtest.dir/Exercise.cpp.o' failed 
make[2]: *** [src/wmathtest/CMakeFiles/wmathtest.dir/Exercise.cpp.o] Error 1 
CMakeFiles/Makefile2:160: recipe for target 'src/wmathtest/CMakeFiles/wmathtest.dir/all' failed 
make[1]: *** [src/wmathtest/CMakeFiles/wmathtest.dir/all] Error 2 
Makefile:76: recipe for target 'all' failed

我创建的类中，operator==和qHash的类。然后我为这个班级创建了一个typedef，但这不起作用。

我在做什么错了？

Tag.h

#ifndef WMATHTEST_TAG_H_ 
#define WMATHTEST_TAG_H_ 

#include <QString> 
#include <QSet> 

namespace WMathTest { 

class Tag { 

public: 

    Tag() = default; 
    Tag(const QString &text); 
    Tag(const Tag &tag) = default; 
    virtual ~Tag() = default; 
    void setText(const QString &text); 
    const QString& getText() const; 
    bool operator==(const Tag &other); 

private: 

QString m_text; 
}; 

} // namespace WMathTest 


inline uint qHash(const WMathTest::Tag &tag, uint seed) { 
    return qHash(tag.getText(), seed); 
} 

typedef QSet<WMathTest::Tag> TagList; 

#endif // !WMATHTEST_TAG_H_

Tag.cpp

#include "wmathtest/Tag.h" 

namespace WMathTest { 

/////////////////////////////////////////////////////////////////////////////// 
// PUBLIC SECTION               // 
/////////////////////////////////////////////////////////////////////////////// 

Tag::Tag(const QString &text) : 
    m_text(text) { 

} 

void Tag::setText(const QString &text) { 
    m_text = text; 
} 

const QString& Tag::getText() const { 
    return m_text; 
} 

bool Tag::operator==(const Tag &other) { 
    return m_text == other.m_text; 
} 

} // namespace WMathTest

Exercise.h

#ifndef WMATHTEST_EXERCISE_H_ 
#define WMATHTEST_EXERCISE_H_ 

#include "wmathtest/LaTeXText.h" 
#include "wmathtest/Tag.h" 
#include <QString> 

namespace WMathTest { 

class Exercise { 

public: 

    Exercise() = default; 
    virtual ~Exercise() = default; 
    void setID(const QString &id); 
    void setProblem(const LaTeXText &problem); 
    void setSolution(const LaTeXText &solution); 
    void addArgumentTag(const Tag &tag); 
    void addArgumentTag(const QString &tag); 
    QString getID() const; 
    LaTeXText getProblem() const; 
    LaTeXText getSolution() const; 
    const TagList& getArgumentTagList() const; 

private: 

    QString m_id; 
    LaTeXText m_problem; 
    LaTeXText m_solution; 
    TagList m_tagList; 
}; 

} // namespace WMathTest 

#endif // !WMATHTEST_EXERCISE_H_

Exercise.cpp

#include "wmathtest/Exercise.h" 

namespace WMathTest { 

/////////////////////////////////////////////////////////////////////////////// 
// PUBLIC SECTION               // 
/////////////////////////////////////////////////////////////////////////////// 

void Exercise::setID(const QString &id) { 
    m_id = id; 
} 

void Exercise::setProblem(const LaTeXText &problem) { 
    m_problem = problem; 
} 

void Exercise::setSolution(const LaTeXText &solution) { 
    m_solution = solution; 
} 

void Exercise::addArgumentTag(const Tag &tag) { 
    m_tagList.insert(tag); 
} 

void Exercise::addArgumentTag(const QString &tag) { 
    m_tagList.insert(Tag(tag)); 
} 

QString Exercise::getID() const { 
    return m_id; 
} 

LaTeXText Exercise::getProblem() const { 
    return m_problem; 
} 

LaTeXText Exercise::getSolution() const { 
    return m_solution; 
} 

const TagList& Exercise::getArgumentTagList() const { 
    return m_tagList; 
} 

} // namespace WMathTest

来源

2015-09-16 Jepessen

似乎错误“/opt/Qt/5.5/gcc_64/include/QtCore/qhash.h:103:5：错误：调用“qHash（常量WMathTest没有匹配功能::因为你定义qHash为“inline uint qHash（const WMathTest :: Tag＆tag，uint seed）”，但QSet希望它被定义为“inline uint qHash（const WMathTest :: Tag＆tag）” –

使用'inline uint qHash（const WMathTest :: Tag＆tag）{return qHash（tag.getText（））;}'我已经在文档http：// doc中看到过使用了它们。 qt.io/qt-5/qhash.html#qhash – Jepessen

散列是一个一元函数（仅一个参数），它是数学意义上的函数（为特定参数返回相同的值，并将为完整参数集返回有效值）。

哈希函数有一个重要条件，必须始终满足才能正常工作：如果两个对象被视为相等，则此对象的哈希值必须相等。因此，举个例子，如果你是什么不区分大小写的容器，其中字符串是关键，你必须提供不区分大小写的散列函数。

请注意qHash functions you are see in documentation的其他参数：seed总是有一个默认值！所以这个函数可以用单个参数调用！这个参数只是一个选项，当您为复杂类型构建自定义散列函数时，您可以调整散列函数。

解决这样的代码：

inline uint qHash(const WMathTest::Tag &tag) { 
    return qHash(tag.getText(), 0xa03f); // arbitrary value 
}

或像这样：

inline uint qHash(const WMathTest::Tag &tag, uint seed = 0) { 
    return qHash(tag.getText(), seed^0xa03f); 
}

在更复杂的类型散列函数的情况下，可能看起来像这样（例如为什么种子可能是有用的）：

inline uint qHash(const DoubleStringValue &tag, uint seed = 0) { 
    return qHash(tag.firstText(), seed^0xa03f)^qHash(tag.secondText(), seed^0x17a317a3); 
}

请注意，这种方式如果有两个DoubleStringValue对象，其中firstText和secondText被翻转后，它们的哈希值将会不同。

我推荐阅读一些有关散列函数容器如何工作的文档，以及它们为什么比替代解决方案（例如红黑树）更快。

来源

2015-09-16 20:58:10

在我的函数中，我用'return qHash（tag.getText（），0xa3e）替换了'return qHash（tag.getText（））;'''获得相同的错误。在文档中写道，我可以声明'uint qHash（const K &key);'，我已经看到'QString'的'qHash'被声明为'uint qt_hash（const QString＆key）Q_DECL_NOTHROW'，所以我没有看到任何编程错误在我的代码中，但显然有一个，因为它不起作用，即使我做了你所说的（我已经做过）。看来根据'qhash.h'，我不需要指定QString的种子，因为它有一个默认值 – Jepessen

@Jepessen你是否声明了默认值为seed？你应该。 –

是的我已经声明了一个默认值 – Jepessen

我自己找到了解决方案。显然这是我的错误，但与我的qHash实现无关。

我已经做了在operator==声明的错误：

bool operator==(const Tag &other);

宣言错过了const预选赛。它应该是

bool operator==(const Tag &other) const;

来源

2015-09-18 08:53:05 Jepessen

QSet：qHash和自定义类出错

回答

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