如何重载operator <<

Question

我试着operator <<在Qt中超载.

class MyCryptographicHash : public QCryptographicHash
{
public:
    MyCryptographicHash(Algorithm method);

    void addData(const QString &data );

    friend MyCryptographicHash& operator<< (MyCryptographicHash &obj, const QString &value);

private:
    QByteArray _data;
};

MyCryptographicHash& operator<<(MyCryptographicHash &obj, const QString &value) {
    obj.addData(value);
    return obj;
}


    MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    MyCryptographicHash *hash1 = new MyCryptographicHash(QCryptographicHash::Sha1);
    MyCryptographicHash *hash2 = new MyCryptographicHash(QCryptographicHash::Sha1);
    hash1->addData("abc1234");
    QString a;
    a = "qweer321";
    hash2<<a;
    qDebug() << "HASH1: " << hash1->result();
    qDebug() << "HASH2: " << hash2->result();
}

但我得到错误:

no match for 'operator<<' in 'hash2 << a'

我试图将运算符声明为类的成员,但也会出错.

error: 'MyCryptographicHash& MyCryptographicHash::operator<<(MyCryptographicHash&, const QString&)' must take exactly one argument

我究竟做错了什么？

Answer 1

你的代码应该是

*hash2 << a;

hash2是一个指针,而不是一个对象.

但是在你发布的代码中,没有明显的理由说 hash2是一个指针.所以你可以写

{
    MyCryptographicHash hash1(QCryptographicHash::Sha1);
    MyCryptographicHash hash2(QCryptographicHash::Sha1);
    hash1.addData("abc1234");
    QString a;
    a = "qweer321";
    hash2 << a;
    qDebug() << "HASH1: " << hash1.result();
    qDebug() << "HASH2: " << hash2.result();
}

这也有不泄漏记忆的优点.

但也许这比你发布的代码更多.