Program crash when a signal is emitted

[croscato]

I have the following class definition:

#ifndef QMYSQLTABLE_H
#define QMYSQLTABLE_H
 
#include <QObject>
#include <QSqlQuery>
 
class QMysqlConnection;
 
class QMysqlTable: public QObject, protected QSqlQuery
{
    Q_OBJECT
 
    friend class QDataLineEdit;
 
public:
    QMysqlTable(const QString& table, const QMysqlConnection* connection,
            QObject* = 0);
 
    bool exec(const QString& query);
    bool isValid(void) const;
 
public slots:
    bool first(void);
    bool previous(void);
    bool next(void);
    bool last(void);
    bool seek(int index, bool relative = false);
 
signals:
    void firstRecord(void);
    void previousRecord(void);
    void nextRecord(void);
    void lastRecord(void);
    void seekRecord(void);
 
private:
    const QMysqlConnection* _connection;
 
    const QString& _table;
};
 
#endif // QMYSQLTABLE_H

#ifndef QMYSQLTABLE_H
#define QMYSQLTABLE_H

#include <QObject>
#include <QSqlQuery>

class QMysqlConnection;

class QMysqlTable: public QObject, protected QSqlQuery
{
    Q_OBJECT

    friend class QDataLineEdit;

public:
    QMysqlTable(const QString& table, const QMysqlConnection* connection,
            QObject* = 0);

    bool exec(const QString& query);
    bool isValid(void) const;

public slots:
    bool first(void);
    bool previous(void);
    bool next(void);
    bool last(void);
    bool seek(int index, bool relative = false);

signals:
    void firstRecord(void);
    void previousRecord(void);
    void nextRecord(void);
    void lastRecord(void);
    void seekRecord(void);

private:
    const QMysqlConnection* _connection;

    const QString& _table;
};

#endif // QMYSQLTABLE_H

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and the implementation part the function next() is:

bool QMysqlTable::next(void)
{
    if (_connection->isValid()) {
        emit nextRecord();
 
        return QSqlQuery::next();
    }
 
    return false;
}

bool QMysqlTable::next(void)
{
    if (_connection->isValid()) {
        emit nextRecord();

        return QSqlQuery::next();
    }

    return false;
}

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the code for the next() function only work if the nextRecord() signal is not emited. Otherwise the program crashes.

What could have been causing this behavior?

Thanks in advance.