Analyze linux program function calling status

function calling status tracing

use linux utilities valgrind (it also can analyze memory leakage) and kcachegrind ui tool to help us analyze function usage status

1. install utilities

in ubuntu system, use the command to install these utilities:

sudo apt install kcachegrind valgrind

2. run the target process

use the valgrind to generate report for calling usage status

valgrind --tool=callgrind <process>

after the command, the report file likes “callgrind.out." should be generated in your folder

3. UI tool

the report document has lots of information, we can use the utility kcachegrind to help us show these information:

kcachegrind callgrind.out.<pid>

Interact between QML and C++ layer

QML and C++

while creating a Qt quick application, it is impossible to avoid communicate between qml and c++, it can be shown like:

there are some methods, and I like the first one:

call c++ code from qml

create object

• a class is inherited from QObject you need create a c++ object and inherited from QObject:

class CInterface : public QObject {
  ...
}

• register class in main.cpp after you created the class, you need register it in main.cpp

#include <QQmlEngine>
...
qmlRegisterType<CInterface>("interface", 1, 0, "interface");

• use in qml finally, you just add the code in your qml file like:

  import interface 1.0
  ...
  interface {
  ...
  }
  

communicate between them

• QT signal and slot

  • c++ signal to qml we assume our object has a signal sigAction like this:

    class CInterface : public QObject {
    ...
    signals:
    void sigAction();
    }
    

then we use it in qml:

interface {
  id: c_interface
  onSigAction: {
    ...
  }
}

• qml signal to c++ we assume our object has a slot slotAction in C++ and a signal sigQml in QML:

  class CInterface : public QObject {
  ...
  public slots:
  void slotAction();
  }
  

and the QML part:

interface {
  id: c_interface
}
...
Component.onCompleted: {
  c_interface.slotAction();
}

• Q_INVOKABLE declaration the Q_INVOKABLE declaration can let QML call c++ method directly: (c++ part)

  class CInterface : public QObject {
  ...
  public:
  Q_INVOKABLE void action();
  }
  

and the QML part:

interface {
  id: c_interface
}
...
Component.onCompleted: {
  c_interface.action();
}

type between qml and c++

there are usually used types between c++ and qml, you can refer here to find you want to use:

call qml from c++

in this case, you have to set the objectName for the object you want to call from c++

Rectangle {
  id: "rect"
  objectName: "rectObj"
  ...
}

then you can find the object from c++

QQuickItem *item = engine.findChild<QQuickItem*>("rectObj");