C++, the compiler is behaving strangely or am I missing something?

Question

Qt

I can't figure out why this code throws an error:

QNetworkRequest request();
request.setRawHeader("", "");

error: request for member 'setRawHeader' in 'request', which is of non-class type 'QNetworkRequest()'

For some reason, the compiler considers this to be a function type declaration. Here is another example

QString s = "test";
QNetworkRequest request(QUrl(s));
request.setRawHeader("", "");

error: request for member 'setRawHeader' in 'request', which is of non-class type 'QNetworkRequest(QUrl)

Working options:

QUrl reqUrl(url);
QNetworkRequest req(reqUrl);

QNetworkRequest req(QUrl("some_url"));

G++ 4.9.2.

Answer 1

The first example is a classic mistake, the compiler is right - you actually wrote a function.
Parentheses are not required to declare a class and call the default constructor.
Even Carmack rode this one :
The fact that ScopedLock lock() is a function declaration and not a parameterless constructor call made me more upset today.

Answer 2

Unfortunately, for the compiler, the second case also looks like a function declaration.
The req function accepting one parameter (for more details, follow the link).
The first option you suggested is a great way out of this situation. You can also write like this:
Upd: I found a detailed description of this error from Meyers.

Answer 3

In the first case, you declared a function, not a class object.
In the second case, there is no such function (setRawHeader(QSting, QString)).
Try like this:

QString s = "test";
QNetworkRequest request(QUrl(s));
request.setRawHeader(QByteArray(""), QByteArray(""));

or like this:

QNetworkRequest request;
request.setRawHeader("", "");

Answer 4

You can use the new universal initialization syntax , ie write curly brackets instead of parentheses. Here 's a note about the difference between x1 and x2 declarations:

T x1; 
T x2();