c++ - CMake 链接时出错

Question

我是 CMake 的新手，我正在尝试使用它来构建一个小的 KDE 应用程序。我必须使用 QTXml 模块，我的程序编译没有问题，但在链接阶段，ld 找不到 QXml 组件...

主要.cpp

#include "test.h"

int main(int argc, char **argv)
{
    return 0;
}

测试.h

#ifndef TEST_H
#define TEST_H

#include <QXmlResultItems>
#include <QString>
#include <QBuffer>
#include <QXmlQuery>

class test {
public:
    test(){}
    ~test(){}
    QXmlResultItems* find ( const QString& node, const QString& xpath );
private:
    QBuffer device_;
};

#endif // TEST_H

测试.cpp

#include "test.h"

QXmlResultItems* test::find ( const QString& node, const QString& xpath )
{
    QXmlResultItems* result = new QXmlResultItems;
    QXmlQuery query;
    query.bindVariable ( "device",&device_ );
    query.setQuery ( "doc($device)/"+node+"/"+xpath );
    query.evaluateTo ( result );
    return result;
}

CMakeLists.cmake

project(qtcmakepb)

find_package(KDE4 REQUIRED)
include (KDE4Defaults)

include_directories( ${KDE4_INCLUDES} ${QT_INCLUDES} )
#Supposed to be useless because of KDE4 REQUIRED and ${QT_INCLUDES}
find_package(Qt4 COMPONENTS QtCore QtXml REQUIRED )


# In this CMakeLists.txt we define which files
# are used to compile the application
set(qtcmakepb_SRCS main.cpp test.cpp)


# Set the name of the application
kde4_add_executable(qtcmakepb ${qtcmakepb_SRCS})

# Select which libraries we need to link to
target_link_libraries(qtcmakepb ${KDE4_KDEUI_LIBS})
target_link_libraries(qtcmakepb ${QT_QTCORE_LIBS})
target_link_libraries(qtcmakepb ${QT_QTXML_LIBS})

# Tell cmake to install the application binary
install(TARGETS qtcmakepb ${INSTALL_TARGETS_DEFAULT_ARGS})

# Install the .desktop file
install( PROGRAMS qtcmakepb.desktop  DESTINATION ${XDG_APPS_INSTALL_DIR} )

make 的输出:

Linking CXX executable qtcmakepb
CMakeFiles/qtcmakepb.dir/test.o: In function `test::find(QString const&, QString const&)':
/home/zelwina/projects/QtCmakePb/src/test.cpp:5: undefined reference to `QXmlResultItems::QXmlResultItems()'
/home/zelwina/projects/QtCmakePb/src/test.cpp:6: undefined reference to `QXmlQuery::QXmlQuery()'
/home/zelwina/projects/QtCmakePb/src/test.cpp:7: undefined reference to `QXmlQuery::bindVariable(QString const&, QIODevice*)'
/home/zelwina/projects/QtCmakePb/src/test.cpp:8: undefined reference to `QXmlQuery::setQuery(QString const&, QUrl const&)'
/home/zelwina/projects/QtCmakePb/src/test.cpp:9: undefined reference to `QXmlQuery::evaluateTo(QXmlResultItems*) const'
/home/zelwina/projects/QtCmakePb/src/test.cpp:10: undefined reference to `QXmlQuery::~QXmlQuery()'
collect2: erreur: ld a retourné 1 code d'état d'exécution
make[2]: *** [src/qtcmakepb] Erreur 1
make[1]: *** [src/CMakeFiles/qtcmakepb.dir/all] Erreur 2
make: *** [all] Erreur 2

我做错了什么？

Answer 1

使用 CMake 的 FindQt4 module ，执行以下操作:

find_package(Qt4 COMPONENTS QtCore QtXml REQUIRED)
include(${QT_USE_FILE})
include_directories(${KDE4_INCLUDES} ${QT_INCLUDES})
target_link_libraries(qtcmakepb ${KDE4_KDEUI_LIBS} ${QT_LIBRARIES})

如果要指定单独的包含目录和库，请将上面的最后两行替换为:

include_directories(${KDE4_INCLUDES}
                    ${QT_QTCORE_INCLUDE_DIR}
                    ${QT_QTXML_INCLUDE_DIR})
target_link_libraries(qtcmakepb
                      ${KDE4_KDEUI_LIBS}
                      ${QT_QTCORE_LIBRARY}
                      ${QT_QTXML_LIBRARY})

你的问题是你没有调用 include(${QT_USE_FILE}) ，那QT_QTCORE_LIBS应该是 QT_QTCORE_LIBRARY (对于 QtXml 库也是如此)。此外，您需要调用 include_directories 之后您调用了 FindQt4 模块和 include dQT_USE_FILE .

有关随您的 CMake 版本提供的 FindQt4 模块的完整信息，请运行:

cmake --help-module FindQt4

编辑

事实证明，根本原因实际上是未定义的函数是 QtXmlPatterns 库的一部分，所以 find_package电话应包括QtXmlPatterns在列表中。

完成后，变量 ${QT_QTXMLPATTERNS_INCLUDE_DIR}和 ${QT_QTXMLPATTERNS_LIBRARY}由调用 include(${QT_USE_FILE}) 设置并且可以根据需要添加。

如果您使用的是 QT5

有了 Qt5，使用 CMake 变得更简单。

为了包含和链接 QtXml 和 QtXmlPatterns，您只需要这些行:

find_package(Qt5Xml REQUIRED)
find_package(Qt5XmlPatterns REQUIRED)

链接如下:

target_link_libraries(qtcmakepb Qt5::Xml Qt5::XmlPatterns)