5

当我将 QUrl 传递给 QNetworkRequest 构造函数时，编译器会出现奇怪的错误。更奇怪的是它只发生在特定情况下，这里有一个例子：

#include <QCoreApplication>
#include <QNetworkReply>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QString str;

    QNetworkRequest req(QUrl(str));
    req.setUrl(QUrl(str)); // error: request for member 'setUrl' in 'req', which is of non-class type 'QNetworkRequest ()(QUrl)'

    QNetworkRequest req2(QUrl(QString("http://google.com"))); // works here perfectly!
    req2.setUrl(QUrl(str));

    QNetworkRequest req3;
    req3.setUrl(QUrl(str));

    QUrl url(str);
    QNetworkRequest req4(url);
    req4.setUrl(QUrl(str));

    return a.exec();
}

g++-4.2 说：

main.cpp:11: error: request for member 'setUrl' in 'req', which is of non-class type 'QNetworkRequest ()(QUrl)'

vs2010 编译器说：

error C2228: left of '.setUrl' must have class/struct/union

当我想将“损坏的” QNetworkRequest 传递给 QNetworkAccessManager::get 方法时，我从 vs2010 得到了额外的解释：

error C2664: 'QNetworkAccessManager::get' : cannot convert parameter 1 from 'QNetworkRequest (__cdecl *)(QUrl)' to 'const QNetworkRequest &'
      Reason: cannot convert from 'overloaded-function' to 'const QNetworkRequest'
      No constructor could take the source type, or constructor overload resolution was ambiguous

多么奇怪..有人有线索吗？也许我只是忘记了如何编程..

4

1 回答 1

10

您遇到了所谓的“令人烦恼的解析”。这个：

QNetworkRequest req(QUrl(str));

相当于

QNetworkRequest req(QUrl str);

这是一个函数声明。

要声明一个变量并从临时初始化它，您需要

QNetworkRequest req{QUrl{str}};                    // C++11
QNetworkRequest req = QNetworkRequest(QUrl(str));  // Historic C++ (if it's copyable)

或使用命名变量而不是临时变量，就像使用req4.

于 2013-10-30T19:05:46.327 回答