QMetaObject Compiler explain?

Question

I am trying to know how Qt implements meta object compiling which enables them to provide signal slot mechanism in Qt. I am not able to finding much details in the documentation.

EDIT::I am not able to get the source code of _id = QObject::qt_metacall(_c, _id, _a);

Following is source file and corresponding moc file.

#ifndef SSOBJECT_H
#define SSOBJECT_H

#include <QObject>

class ssObject : public QObject
{
Q_OBJECT
public:
    explicit ssObject(QObject *parent = 0);

signals:
    void readyToPrint();
    void readyToPrint1(int);
    void readyToPrint2(float);

private slots:
    int print();

};

#endif // SSOBJECT_H

//output from MOC
#include "../ssobject.h"
#if !defined(Q_MOC_OUTPUT_REVISION)
#error "The header file 'ssobject.h' doesn't include <QObject>."
#elif Q_MOC_OUTPUT_REVISION != 62
#error "This file was generated using the moc from 4.6.1. It"
#error "cannot be used with the include files from this version of Qt."
#error "(The moc has changed too much.)"
#endif

QT_BEGIN_MOC_NAMESPACE
static const uint qt_meta_data_ssObject[] = {

 // content:
       4,       // revision
       0,       // classname
       0,    0, // classinfo
       4,   14, // methods
       0,    0, // properties
       0,    0, // enums/sets
       0,    0, // constructors
       0,       // flags
       3,       // signalCount

 // signals: signature, parameters, type, tag, flags
      10,    9,    9,    9, 0x05,
      25,    9,    9,    9, 0x05,
      44,    9,    9,    9, 0x05,

 // slots: signature, parameters, type, tag, flags
      69,    9,   65,    9, 0x08,

       0        // eod
};

static const char qt_meta_stringdata_ssObject[] = {
    "ssObject\0\0readyToPrint()\0readyToPrint1(int)\0"
    "readyToPrint2(float)\0int\0print()\0"
};

const QMetaObject ssObject::staticMetaObject = {
    { &QObject::staticMetaObject, qt_meta_stringdata_ssObject,
      qt_meta_data_ssObject, 0 }
};

#ifdef Q_NO_DATA_RELOCATION
const QMetaObject &ssObject::getStaticMetaObject() { return staticMetaObject; }
#endif //Q_NO_DATA_RELOCATION

const QMetaObject *ssObject::metaObject() const
{
    return QObject::d_ptr->metaObject ? QObject::d_ptr->metaObject : &staticMetaObject;
}

void *ssObject::qt_metacast(const char *_clname)
{
    if (!_clname) return 0;
    if (!strcmp(_clname, qt_meta_stringdata_ssObject))
        return static_cast<void*>(const_cast< ssObject*>(this));
    return QObject::qt_metacast(_clname);
}

int ssObject::qt_metacall(QMetaObject::Call _c, int _id, void **_a)
{
    _id = QObject::qt_metacall(_c, _id, _a);
    if (_id < 0)
        return _id;
    if (_c == QMetaObject::InvokeMetaMethod) {
        switch (_id) {
        case 0: readyToPrint(); break;
        case 1: readyToPrint1((*reinterpret_cast< int(*)>(_a[1]))); break;
        case 2: readyToPrint2((*reinterpret_cast< float(*)>(_a[1]))); break;
        case 3: { int _r = print();
            if (_a[0]) *reinterpret_cast< int*>(_a[0]) = _r; }  break;
        default: ;
        }
        _id -= 4;
    }
    return _id;
}

// SIGNAL 0
void ssObject::readyToPrint()
{
    QMetaObject::activate(this, &staticMetaObject, 0, 0);
}

// SIGNAL 1
void ssObject::readyToPrint1(int _t1)
{
    void *_a[] = { 0, const_cast<void*>(reinterpret_cast<const void*>(&_t1)) };
    QMetaObject::activate(this, &staticMetaObject, 1, _a);
}

// SIGNAL 2
void ssObject::readyToPrint2(float _t1)
{
    void *_a[] = { 0, const_cast<void*>(reinterpret_cast<const void*>(&_t1)) };
    QMetaObject::activate(this, &staticMetaObject, 2, _a);
}
QT_END_MOC_NAMESPACE

Also explain how QObject::connect(ssobj1,SIGNAL(readyToPrint()),ssobj1,SLOT(print())) expands

Answer 1

The best way to figure this out is to download the source code and have a look.

Answer 2

You'll find some of the answers here.