Qt下载http文件

这是一个有问题的版本： 

class download_file :public QObject{
    Q_OBJECT;
public:
    download_file(QString url, QString path);
    void sendRequest();
public slots:
    void requestFinished(QNetworkReply* reply);
protected:
    QNetworkAccessManager* httpMgr;
private:
    QString url, path;
};

download_file::download_file(QString url,QString path)
{
    this->url = url;
    this->path = path;
}
void download_file::sendRequest()
{
    httpMgr = new QNetworkAccessManager(this);
    QObject::connect(httpMgr, SIGNAL(finished(QNetworkReply*)), this, SLOT(requestFinished(QNetworkReply*)));
    QNetworkRequest requestInfo;
    requestInfo.setUrl(QUrl(url));
    QNetworkReply *reply = httpMgr->get(requestInfo);
}
void download_file::requestFinished(QNetworkReply* reply)
{
    QVariant statusCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
    if (statusCode.isValid())
        qDebug() << "status code=" << statusCode.toInt();

    QVariant reason = reply->attribute(QNetworkRequest::HttpReasonPhraseAttribute).toString();
    if (reason.isValid())
        qDebug() << "reason=" << reason.toString();

    QNetworkReply::NetworkError err = reply->error();
    if (err != QNetworkReply::NoError) {
        qDebug() << "Failed: " << reply->errorString();
    }
    else {
        // 获取返回内容
        QByteArray ba(reply->readAll());
        //qDebug() << ba;
        //保存
        QFile file(path);
        bool ok = file.open(QIODevice::WriteOnly);
        if(ok){
            file.write(ba);
            file.close();
        }
        else {
            qDebug() << "open failed!";
        }
    }
}

当要下载的文件过大时，程序会崩溃！！！(std::bad_alloc)（所以只可以下载一些小的文件）

我认为这是ba(QByteArray)太大了，要一下子往文件中写入太多的数据，导致new失败了。

修复：

Qt 基于http的网络文件下载_qt http下载文件-CSDN博客(参考+引用）

class download_file :public QObject{
    Q_OBJECT;
public:
    download_file(QString url, QString path);
    void sendRequest();
public slots:
    void on_finished();
    void on_readyRead();
    void on_downloadProgress(qint64 bytesRead, qint64 totalBytes);
protected:
    QNetworkAccessManager* httpMgr;
private:
    QString url, path;
    QFile* file;
    QNetworkReply* reply;
};

download_file::download_file(QString url,QString path)
{
    this->url = url;
    this->path = path;
}
void download_file::sendRequest()
{
    httpMgr = new QNetworkAccessManager(this);

    QNetworkRequest requestInfo;
    requestInfo.setUrl(QUrl(url));
    PRINTF_LOCATION() << url;
    reply = httpMgr->get(requestInfo);
    connect(reply, &QNetworkReply::finished, this, &download_file::on_finished);
    connect(reply, &QNetworkReply::readyRead, this, &download_file::on_readyRead);
    connect(reply, &QNetworkReply::downloadProgress, this, &download_file::on_downloadProgress);
    file = new QFile(path);
    if (!file->open(QIODevice::WriteOnly))
        return;

}
void download_file::on_finished()
{
    file->close();
    delete file;
    file = nullptr;

    reply->deleteLater();
    reply = nullptr;
}
void download_file::on_downloadProgress(qint64 bytesRead, qint64 totalBytes)
{
    qDebug() << bytesRead << "   " << totalBytes;
}
void download_file::on_readyRead()
{
    file->write(reply->readAll());
}