我有一个相当大的 struct称为 Journey :
typedef struct Journey
{
/**
* @brief The InfoText struct is a container for storing messages (short and long) that are found
* inside a journey's <InfoTextLists/> as <InfoText/> elements
*/
typedef struct InfoText
{
QString shortMsg;
QString longMsg;
InfoText(QString shortMsg, QString longMsg)
{
this->shortMsg = shortMsg;
this->longMsg = longMsg;
}
bool operator ==(const InfoText &other)
{
return (this->shortMsg == other.shortMsg) && (this->longMsg == other.longMsg);
}
bool operator !=(const InfoText &other)
{
return !(*this == other);
}
} InfoText;
QTime arrivalNextImmediateStop; //!< Arrival time (planned). It can be found under Time inside Arr in XML reply
QTime arrivalNextImmediateStopRelative; //!< Arrival time (relative, @p arrivalNextImmediateStop + @p delay)
// Departure data
QTime departure; //!< Departure time (planned). It can be found under Time inside Dep in XML reply
quint32 departureRelative; //!< Departure time (relative and in minutes, @p departure + @p delay - current time)
int delay; //!< Departure time delay (minutes). It can be found under Delay inside Dep in XML reply
// Transfer time
// TODO Calculate this at the beginning of the data fusion slotGetData(). It is required for the display of the connection (remaining time column)
QTime transferTime; //!< Transfer time based on the CSV L and V files. Required for the lookup filter (see @ref Data::Filtering::FilterFutureLookup)
// Direction and destination data
quint8 direction; //!< Run direction (1, 2). It can be found under Attribute of type DIRECTIONFLAG in XML reply
QString directionTarget; //!< Run direction final destination. It can be found under Attribute of type DIRECTION in XML reply
QString operatorJ; //!< Full name of operator of the journey (Berliener Verkehrsbetriebe, DB Regio AG ...). It can be found under Attribute of type OPERATOR in XML reply
QString vehicleType; //!< Type of the vehicle (B, F, U, S ...). It can be found under Attribute with of type CATEGORY in XML reply
QString line; //!< The line of the vehicle (for example: 109 (for Bus 109), S5 (for S-Bahn 5) etc.). It can be found under Attribute of type NUMBER in XML reply
// Immedidate stops data
quint32 immediateStop1; //!< First immediate stop ID (without offset) after current station
quint32 immediateStop2; //!< Second immediate stop ID (without offset) after current stations
bool dirty; //!< Used by the secondary filtering mechanism this value shows whether the given connection has been marked for removal or not
/**
* @brief Stores all <InfoText/> element found inside the journey's <InfoTextLists/> element. An info text is a message consisting of a headline (short message)
* and a body (long message)
*/
QList<InfoText> infoTexts;
/**
* @brief Constructor
*/
Journey()
{
this->arrivalNextImmediateStop = QTime();
this->arrivalNextImmediateStop = QTime();
this->departure = QTime();
this->departureRelative = 0;
this->transferTime = QTime();
this->delay = this->direction = this->immediateStop1 = this->immediateStop2 = 0;
this->directionTarget = this->operatorJ = this->vehicleType = this->line = "";
this->dirty = false;
}
/**
* @brief Allows comparing for equality between two journeys
* @param other Journey to compare with
* @return True if arrival time to both next two immediate stops, departure time, relative departure
* time, delay, direction, destination, journey operator, vehicle type, line and IDs of next
* two immediate stops are equal
*/
bool operator ==(const Journey &other)
{
return arrivalNextImmediateStop == other.arrivalNextImmediateStop
&& arrivalNextImmediateStopRelative == other.arrivalNextImmediateStopRelative
&& departure == other.departure
&& departureRelative == other.departureRelative
&& delay == other.delay
&& direction == other.direction
&& directionTarget == other.directionTarget
&& operatorJ == other.operatorJ
&& vehicleType == other.vehicleType
&& line == other.line
&& immediateStop1 == other.immediateStop1
&& immediateStop2 == other.immediateStop2;
}
/**
* @brief Allows comparing for inequality between two journeys
* @param other
* @return True if arrival time to both next two immediate stops, departure time, relative departure
* time, delay, direction, destination, journey operator, vehicle type, line and IDs of next
* two immediate stops are not equal
*/
bool operator !=(const Journey &other)
{
return !(*this == other);
}
/**
* @brief Overloads the < operator to allow sorting journeys in a ascending order based on their line. Due to the alphanumeric nature of
* most lines special handling is required to ensure proper order. With the default string comparison namely own_line < other_line the result
* is in most cases not correct: M10, M5, M8 instead of M5, M8, M10. Using @ref alphanumericLineSplitRx an attempt is made to split the line
* into two distrinctive tokens - alphabetic and numeric. If the split does not succeed the line is made only of letter or digits in which case
* standard string comparison can be used. On the other hand if it does succeed, we need to do a comparison of each of the two tokens. In some
* cases lines can be the same in which case the direction of both is used for the comparison
* @param other A journey with a line
* @return True if line of journey is smaller (string comparison or numeric comparison if lines are of alphanumeric or only numeric nature) than line of @p journey
*/
bool operator < (const Journey &other)
{
QRegularExpressionMatch matchesOwn = alphanumericLineSplitRx.match(this->line);
QRegularExpressionMatch matchesOther = alphanumericLineSplitRx.match(other.line);
// Figure out if the lines of our own and the other journey are complex (alphanumeric) or simple (just alphabetic or just numeric)
// If we have alphanumeric lines we need to split each line into two tokens - alphabetic and numeric
if (matchesOwn.capturedTexts().length() == 3 && matchesOther.capturedTexts().length() == 3)
{
QString lineAlphaOwn = matchesOwn.captured(1);
QString lineAlphaOther = matchesOther.captured(1);
quint16 lineNumericOwn = matchesOwn.captured(2).toUInt();
quint16 lineNumericOther = matchesOther.captured(2).toUInt();
// If the alphabetic token of both journies are different there is not need to compare the numeric token and
// standard string comparison is used
// Example: N20, M100 will be sorted as M100, N20 since M comes before N
if (lineAlphaOwn != lineAlphaOther)
{
return this->line < other.line;
}
// If the alphabetic token is the same for both lines the numeric token is the next criterion for sorting
// Example: N10, N1, N2, N20 will be sorted as N1, N2, N10, N20
if (lineNumericOwn != lineNumericOther)
{
return lineNumericOwn < lineNumericOther;
}
// If both the alphabetic and the numeric tokens are the same the direction will be used as the sorting criterion
// Example: N10 (direction 2), N10 (direction 1) will be sorted as N10 (direction 1), N10 (direction 2)
return this->direction < other.direction;
}
// In case the matching has failed this means that the line consists either of just a single alphabetic or numeric
// The numeric-only case needs to be handled to avoid sorting results like 1, 100, 1000, 2, 20, 2000 ...
bool isOwnNumericOnly = false;
bool isOtherNumericOnly = false;
quint16 lineNumericOwn = matchesOwn.captured(1).toUInt(&isOwnNumericOnly);
quint16 lineNumericOther = matchesOther.captured(1).toUInt(&isOtherNumericOnly);
if (isOwnNumericOnly && isOtherNumericOnly)
{
// In case the line (digits only!) of both journies are different, we use standard numeric comparison
// Example: 206, 815, 413 will be sorted as 206, 413, 815
if (lineNumericOwn != lineNumericOther)
{
return lineNumericOwn < lineNumericOther;
}
// Both journies have the same number for a line so the direction is used as the sorting criterion
// Example: 280 (direction 2), 280 (direction 1) will be sorted as 280 (direction 1), 280 (direction 2)
return this->direction < other.direction;
}
else
{
// In case the line (letters only!) of both journies are different, we use standard string comparison
// Example: S, TXL, R will be sorted as R, S, TXL
if (this->line != other.line)
{
return this->line < other.line;
}
// Both journies have the same letter for a line so the direction is used as the sorting criterion
// Example: TXL (direction 2), TXL (direction 1) will be sorted as TXL (direction 1), TXL (direction 2)
return this->direction < other.direction;
}
}
/**
* @brief Overloads the > operator to allow sorting journeys in a ascending order based on their line. Internally the overloaded
* @ref operator < and @ref operator != operators are used
* @param other A journey with a line
* @return True if line of journey is greater (string comparison or numeric comparison if lines are of alphanumeric or only numeric nature) than line of @p journey
*/
bool operator > (const Journey &other)
{
return (*this != other) && (*this < other);
}
/**
* @brief Checks if the journey belongs to a specific vehicle type
* @param vehicleType Type of vehicle to check own affiliation with
* @return True if journey belongs to @p vehicleType
*/
bool belongsToVehicleType(QString vehicleType)
{
return this->vehicleType == vehicleType;
}
} Journey;
它存储从服务器的 HTTP GET 回复中检索到的数据，该服务器提供有关各种车辆及其穿过城市的路线的信息。
我正在使用的规范中的一项要求在我过滤了一次无效(基于各种标准)后导致了庞大的重载 < 之后，为旅程提供了一个不那么简单的排序机制。您在上面的代码片段中看到的运算符(其他在这里并不重要)。
我必须将所有可用行程分成更小的组(根据车辆类型，这就是 belongsToVehicleType() 函数的用途)。对于每组旅程，我必须运行 std::sort以实现该数据所需的顺序。
长话短说 - 在我的本地机器(32 位 Ubuntu 16.04 和 Qt 5.4.2)上一切正常，但是当我尝试交叉编译它时(目标系统也使用 Qt 5.4.2，基于 Intel 的 32 位架构等.).请注意，如果我注释掉所有我称之为 std::sort() 的行即使使用交叉编译器，我的代码似乎也能正常编译(尽管链接器提示由于某种原因无法找到 libc.so.6)。您可以在下面看到 Qt Creator 输出的错误消息:
/opt/target-toolchain/crosstools/i686-unknown-linux-gnu/i686-unknown-linux-gnu/include/c++/4.7.4/bits/stl_algo.h:2277: error: passing 'const Data::Journey' as 'this' argument of 'bool Data::Journey::operator<(const Data::Journey&)' discards qualifiers [-fpermissive]
当我调用 std::sort 时出现此错误在任何QList与各自的旅程有关。例如:
QList<Journey> connectionsRE;
// Fill connectionsRE
if (connectionsRE.length())
{
LOG(INFO) << "Regional train (Express) RE1-RE9 connections:";
std::sort(connectionsRE.begin(), connectionsRE.end()); // <----------- ERROR STARTS FROM HERE!!!
// Do something else with connectionsRE
}
运行时的完整编译错误make在项目的构建文件夹中是
In file included from /opt/target-toolchain/crosstools/i686-unknown-linux-gnu/lib/gcc/i686-unknown-linux-gnu/4.7.4/../../../../i686-unknown-linux-gnu/include/c++/4.7.4/algorithm:63:0,
from /opt/target-toolchain/Qt/Qt5/include/QtCore/qglobal.h:81,
from /opt/target-toolchain/Qt/Qt5/include/QtCore/qnamespace.h:37,
from /opt/target-toolchain/Qt/Qt5/include/QtCore/qobjectdefs.h:41,
from /opt/target-toolchain/Qt/Qt5/include/QtCore/qobject.h:40,
from /opt/target-toolchain/Qt/Qt5/include/QtCore/QObject:1,
from /home/user/Projects/project/src/datafusionhandler.h:4,
from /home/user/Projects/project/src/datafusionhandler.cpp:1:
/opt/target-toolchain/crosstools/i686-unknown-linux-gnu/lib/gcc/i686-unknown-linux-gnu/4.7.4/../../../../i686-unknown-linux-gnu/include/c++/4.7.4/bits/stl_algo.h: In instantiation of '_RandomAccessIterator std::__unguarded_partition(_RandomAccessIterator, _RandomAccessIterator, const _Tp&) [with _RandomAccessIterator = QList<Data::Journey>::iterator; _Tp = Data::Journey]':
/opt/target-toolchain/crosstools/i686-unknown-linux-gnu/lib/gcc/i686-unknown-linux-gnu/4.7.4/../../../../i686-unknown-linux-gnu/include/c++/4.7.4/bits/stl_algo.h:2315:70: required from '_RandomAccessIterator std::__unguarded_partition_pivot(_RandomAccessIterator, _RandomAccessIterator) [with _RandomAccessIterator = QList<Data::Journey>::iterator]'
/opt/target-toolchain/crosstools/i686-unknown-linux-gnu/lib/gcc/i686-unknown-linux-gnu/4.7.4/../../../../i686-unknown-linux-gnu/include/c++/4.7.4/bits/stl_algo.h:2347:54: required from 'void std::__introsort_loop(_RandomAccessIterator, _RandomAccessIterator, _Size) [with _RandomAccessIterator = QList<Data::Journey>::iterator; _Size = int]'
/opt/target-toolchain/crosstools/i686-unknown-linux-gnu/lib/gcc/i686-unknown-linux-gnu/4.7.4/../../../../i686-unknown-linux-gnu/include/c++/4.7.4/bits/stl_algo.h:5483:4: required from 'void std::sort(_RAIter, _RAIter) [with _RAIter = QList<Data::Journey>::iterator]'
/home/user/Projects/project/src/datafusionhandler.cpp:387:61: required from here
/opt/target-toolchain/crosstools/i686-unknown-linux-gnu/lib/gcc/i686-unknown-linux-gnu/4.7.4/../../../../i686-unknown-linux-gnu/include/c++/4.7.4/bits/stl_algo.h:2277:4: error: passing 'const Data::Journey' as 'this' argument of 'bool Data::Journey::operator<(const Data::Journey&)' discards qualifiers [-fpermissive]
compilation terminated due to -Wfatal-errors.
src/CMakeFiles/project.dir/build.make:134: recipe for target 'src/CMakeFiles/project.dir/datafusionhandler.cpp.o' failed
make[2]: *** [src/CMakeFiles/project.dir/datafusionhandler.cpp.o] Error 1
CMakeFiles/Makefile2:1018: recipe for target 'src/CMakeFiles/project.dir/all' failed
make[1]: *** [src/CMakeFiles/project.dir/all] Error 2
Makefile:94: recipe for target 'all' failed
make: *** [all] Error 2
-Wfatal-errors为我的本地机器和目标系统的build设置。也许我的 rootfs 目录(存储目标操作系统镜像的位置)中的某些底层库太旧了？
最佳答案
我认为您可能需要将某些运算符函数声明为 const，例如:
bool operator > (const Journey &other) const
{
...
}
关于linux - 在结构列表上调用 std::sort 时将 const 作为 'this' 参数错误传递，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/47576227/