CMake error while linking

Question

I'm quite new to CMake and I'm trying to use it to build a little KDE application. I've to use QTXml module, my program compile with no problem but during the linking phase, ld fail to find QXml components... main.cpp ``` #include "test.h" int main(int argc, char **argv) { return 0; } ``` test.h ``` #ifndef TEST_H #define TEST_H #include #include #include #include class test { public: test(){} ~test(){} QXmlResultItems* find ( const QString& node, const QString& xpath ); private: QBuffer device_; }; #endif // TEST_H ``` test.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_directorie…

Accepted Answer

To use CMake's FindQt4 module, do the following:

```
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})
```

If you want to specify the individual include dirs and libraries, then replace the last 2 lines above with:

```
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})
```

Your problem is that you're not calling `include(${QT_USE_FILE})`, and that `QT_QTCORE_LIBS` should be `QT_QTCORE_LIBRARY` (and similarly for QtXml library). Furthermore, you need to call `include_directories` after you've invoked the FindQt4 module and `include`d the `QT_USE_FILE`.

For full info on the FindQt4 module provided with your version of CMake, run:

```
cmake --help-module FindQt4
```

EDIT

Turns out that the root cause is actually that the undefined functions are part of the QtXmlPatterns library, so the `find_package` call should include `QtXmlPatterns` in the list.

When this is done, the variables `${QT_QTXMLPATTERNS_INCLUDE_DIR}` and `${QT_QTXMLPATTERNS_LIBRARY}` are set by the call `include(${QT_USE_FILE})` and can be added as required.

IF YOU'RE USING QT5

With Qt5, using CMake becomes simpler.

In order to include and link QtXml and QtXmlPatterns, you only need these lines:

```
find_package(Qt5Xml REQUIRED)
find_package(Qt5XmlPatterns REQUIRED)
```

And linking as follows:

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

CMake error while linking

Solution

Problem