我想创建一个我想在程序中使用的QSet<Tag>。 Tag是我的自定义类。
当我构建代码时，我获得了有关qHash重载的gcc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
我已经为班级创建了班级operator==和qHash。然后我为课程创建了typedef，但这不起作用。
我做错了什么？
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
答案 0 :(得分：5)
散列是一元函数（仅一个参数），它是一个数学意义上的函数（为特定参数返回相同的值，并将返回完整参数集的有效值）。
散列函数有一个必须始终满足才能正常工作的重要条件：如果两个对象被认为是相等的，则此对象的散列值也必须相等。因此，例如，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哈希函数。
请注意，qHash functions you are see in documentation的其他参数：seed始终具有默认值！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，它为您提供了在为复杂类型构建自定义哈希函数时调整哈希函数的机会。
修复你的代码：
inline uint qHash(const WMathTest::Tag &tag) {
return qHash(tag.getText(), 0xa03f); // arbitrary value
}
或者像这样：
inline uint qHash(const WMathTest::Tag &tag, uint seed = 0) {
return qHash(tag.getText(), seed^0xa03f);
}
如果更复杂的类型哈希函数可能看起来像这样（示例为什么种子可能有用）：
inline uint qHash(const DoubleStringValue &tag, uint seed = 0) {
return qHash(tag.firstText(), seed^0xa03f)^qHash(tag.secondText(), seed^0x17a317a3);
}
请注意，如果有两个DoubleStringValue对象，其中firstText和secondText被翻转，则两者的哈希值都会有所不同。
我建议阅读一些关于散列函数容器如何工作的文档，以及为什么它们比替代解决方案更快（例如红黑树）。
答案 1 :(得分：2)
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。
我在operator==声明中做错了：
bool operator==(const Tag &other);
声明错过const限定符。它应该是
bool operator==(const Tag &other) const;