QHttpServer: use function pointer as ViewHandler

[JonB]

@Tarae
Yep, that's pretty complex!

Wait for @jsulm's better reply, but maybe you are required to put in the two optional parameters for this free/C function to be acceptable? Worth a try?

[Tarae]

@JonB As you suggested, I've tried this:

const char * responseFunction(const QHttpServerRequest & request, QHttpServerResponder && responder)
{
  return "Hello world!";
}

Still doesn't compile, same error.

[jsulm]

@Tarae said in QHttpServer: use function pointer as ViewHandler:

const char * responseFunction

Try without const:

char * responseFunction(...

[Tarae]

@jsulm No, const char *, char *, QString, const QString, QByteArray, const QByteArray. Still same error.

[JonB]

@Tarae
I'm only guessing, but since those parameters are optional try specifying defaults for them. Assuming you can do that in a free/C function, I don't know.

The const char * for the return value is correct.

BTW: if all else fails, you can always make it a lambda like the examples show and have that lambda simply call your free function....

[Tarae]

@JonB specifying defaults for const QHttpServerRequest & and QHttpServerResponder && is not that easy. But I don't feel like it will solve my problem.
I know I can use a lambda to call my function, but the documentation says function pointer, so I want to figure it out.

[Christian Ehrlicher]

From my pov a plain function is currently not possible so either the documentation is wrong or the implementation. Since there is an easy workaround for it I would guess the solution is to adjust the documentation. Please create a bug report for it and post the bug number here.

[JonB]

If this is what @Christian-Ehrlicher says, no wonder we could not figure it yesterday! :)

[Christian Ehrlicher]

A plain function does not work but a std::function<> since the template magic expects a callable:

std::function<const char* ()>  resp = &responseFunction;
server.route("/", resp);

[JonB]

@Christian-Ehrlicher
I am whistling in the dark here, but I'm a student of C++ so I am interested. I am not as expert as you. The issue is "a callable". I do not have Qt6 so cannot test QHttpServer::route() If you don't want to use a lambda or std::function here, could you use something like:

struct callable
{
  const char *operator()() const
  {
    std::cout << "Hello World from a callable!\n";
    return "Hello World!";
  }
};

const callable responseFunction;
server.route("/", &responseFunction);

Maybe this is the sort of thing a lambda or std::function() does which is different from a plain function?

[Tarae]

@Christian-Ehrlicher I've created a bug report: https://bugreports.qt.io/browse/QTBUG-112484

[Christian Ehrlicher]

And fixed