Macro expansion in moc

I'd like to store some class info using Q_CLASSINFO macro. However I would like to wrap it in my own macro, for example:

#define DB_TABLE( TABLE ) \
    Q_CLASSINFO( "db_table", #TABLE )

#define DB_FIELD( PROPERTY, COLU开发者_开发技巧MN ) \
    Q_CLASSINFO( "dbcol_" #PROPERTY, #COLUMN )

class Foo : public QObject
{
    Q_OBJECT
    DB_TABLE( some_table )
    DB_FIELD( clientName, client_name )
}

Unfortunately, moc doesn't expand macros so the Q_CLASSINFO is not added.

I've tried to feed moc with already preprocessed source, but it failes on some included Qt classes.

Do you know any workaround for this?

The easy way to make that is modifing moc preprocessor.

1. Go to Qt source code to qtbase/src/tools/moc e.g. (C:\Qt\Qt5.0.1\5.0.1\Src\qtbase\src\tools\moc)
2. Create a new copy of moc project e.g. moc_modified
3. Open the copy of moc project with QtCreator (moc.pro file)
4. Open preprocessor.cpp file and go to Symbols Preprocessor::preprocessed(const QByteArray &filename, QIODevice *file) function

5. Search the line:

   // phase 1: get rid of backslash-newlines
   input = cleaned(input);
   
   // <- insert your code to modify input variable
   // input is a QByteArray object that contents the source code of .h file than moc is processing
   // I had created the replaceCustomMacros function, see next line
   replaceCustomMacros(input);
   ...
   

6. Compile the new source code. The moc executable file is generated to /bin folder (if you use windows look at c:/bin/moc.exe)

7. Go to Qt bin (C:\Qt\Qt5.0.1\5.0.1\msvc2010\bin) folder and rename moc executable file e.g. moc.exe.bak

8. Copy new moc executable file to Qt bin folder.

9. In your current app you need to create a Macro for example:

   #ifndef Q_MOC_RUN
   #define DB_FIELD( PROPERTY, COLUMN )
   #endif
   
   //or in my case
   
   #ifndef Q_MOC_RUN
   #define Q_SERVICE_INFO(method, path, type)
   #endif
   

Finally I let you my own source code of function replaceCustomMacros:

This function convert Q_SERVICE_INFO(method, path, type) macro to Q_CLASSINFO("srv://method", "type:path")

void Preprocessor::replaceCustomMacros(QByteArray &source)
{
    QString str(QLatin1String(source.data()));
    QString param_exp(QLatin1String("([^,\n]+)"));
    QByteArray expression("Q_SERVICE_INFO\\s*\\(");
    expression
        .append(param_exp.toLatin1())
        .append(",")
        .append(param_exp.toLatin1())
        .append("(,")
        .append(param_exp.toLatin1())
        .append(")?\\)");
    QRegExp *reg_ex = new QRegExp(QLatin1String(expression));
    int pos = -1, offset = -1, len = str.length();
    while ((offset = reg_ex->lastIndexIn(str, pos)) != -1)
    {
            reg_ex->cap(1);
            pos = -(len - offset) - 1;

            QString capturedString = reg_ex->capturedTexts().at(0);

            QString pattern = capturedString;
            pattern.remove(0, pattern.indexOf(QLatin1String("(")) + 1);
            pattern.remove(pattern.length() - 1, 1);
            QStringList params = pattern.split(QLatin1String(","));

            QString method = params.at(0).trimmed();
            method = method.mid(1, method.length() - 2);

            QString type;
            if (params.length() < 3)
            {
                type.append(QLatin1String("GET"));
            }
            else
            {
                type = params.at(2).trimmed();
                type = type.mid(1, type.length() - 2);
            }

            QString path = params.at(1).trimmed();
            path = path.mid(1, path.length() - 2);

            source.replace(offset, capturedString.length(), QString(QLatin1String("Q_CLASSINFO(\"srv://%1\",\"%2:%3\")")).arg(method, type, path).toLatin1());
    }
    delete reg_ex;

}

I have not found any specific solution on Internet then I have posted this solution.

Good Luck :)

Other than rolling your own pre-moc preprocessor, no. That is what MeeGo Touch does, for example. Since Nokia themselves are doing it, I believe there is no other way.

In your case, it would only involve translating your own declarations into Q_CLASSINFO, so it shouldn't be too hard. If you use qmake, it can be added to the build sequence, too.