'QOverload' was not declared in this scope

Anonymous_Banned275

What did I miss in my code ?

  #include <QtGlobal>

    connect(ui->list,                                   // list_widget_1,
            &QListWidget::itemClicked,
            ui->list_2,                                // list_widget_2,
            QOverload<QListWidgetItem*>::of(&QListWidget::addItem));

c/media/f/QT/Qt/QT/qtconnectivity/examples/bluetooth/CAT_BT_18112020/device.cpp:136: error: 'QOverload' was not declared in this scope
             QOverload<QListWidgetItem*>::of(&QListWidget::addItem));
             ^ode_text

Gojir4

@AnneRanch Hi, This may caused by the C++ version you are using. The doc says:

qOverload() requires C++14 enabled. In C++11-only code, the helper classes QOverload, QConstOverload, and QNonConstOverload can be used directly

jsulm

@Gojir4 OP uses QOverload.

@AnneRanch What Qt version do you use?

aha_1980

@AnneRanch

And to add to @jsulm: Is your compiler C++11 enabled, and do you have CONFIG+=C++11 in your .pro file?

Regards

Anonymous_Banned275

@Gojir4 I;ll check the compiler version.
My guess is C++ 11 so far had no reason to check it.

I am not sure I really need the overload.

I did read the doc, but I did not get what does "using directly " means.

After adding

added CONFIG+=C++11 2/1/2/2020

CONFIG+=C++11

I get this weird error

/media/f/QT/Qt/QT/qtconnectivity/examples/bluetooth/CAT_BT_18112020/service.h:54: error: 'NULL' was not declared in this scope
#define nullptr NULL
^
can I add
#define NULL
to .pro file instead to my "project common" header?
It cannot work / be added directly since "#" is a comment symbol in project file .

JKSH

@AnneRanch said in 'QOverload' was not declared in this scope:

I get this weird error

/media/f/QT/Qt/QT/qtconnectivity/examples/bluetooth/CAT_BT_18112020/service.h:54: error: 'NULL' was not declared in this scope

It's expected, not weird.

C++11 encourages all programmers to move away from NULL. One of the ways it does this is by making it harder to use NULL: https://stackoverflow.com/questions/462165/error-null-was-not-declared-in-this-scope

Note: Whenever you get an error message that seems weird, just copy and paste that message into a search engine. Chances are someone has already explained online how to handle it.

can I add
#define NULL
to .pro file instead to my "project common" header?

You can't (and shouldn't) try something like that. nullptr and NULL are standard components of C++ so you can break things by trying to define them manually.

Just remove the custom #defines in your code and replace all uses of NULL with nullptr.

This article explains why you should switch to nullptr: https://www.cprogramming.com/c++11/c++11-nullptr-strongly-typed-enum-class.html

Anonymous_Banned275

@JKSH So C++ examples of Qt complains about missing null pointer, hence I added #define . Now C++11 complain about it lead me to believe NULL is not even defined.
Funny part NULL is never (openly) used in Qt examples.

"just copy and paste that message into a search engine"

FYI my favorite no-nos in TECHNICAL forum posts:

...Google it ...
...RTFM...
...you needs to study...

I instead prefer to discuss technical stuff in forum and I believe the "no-nos" are pretty given - so why bother to post them?

That is my opinion , so go ahead and ban me...

JKSH

@AnneRanch said in 'QOverload' was not declared in this scope:

Funny part NULL is never (openly) used in Qt examples.

That's a good thing. NULL should not be used anymore, as explained in my previous post and in the links I provided. Does that make sense?

So C++ examples of Qt complains about missing null pointer

That's because your project was not being compiled with C++11 compliance enabled.

What compiler version and Qt version are you using? Recent versions should already have C++11 (or even C++14/C++17) enabled by default, so they should all know nullptr by default even if you don't add CONFIG += C++11.

hence I added #define .

Enabling C++11 to enable the native nullptr keyword is better than adding a custom #define.

That is my opinion , so go ahead and ban me...

You didn't do anything wrong so nobody is gonna ban you.

"just copy and paste that message into a search engine"

FYI my favorite no-nos in TECHNICAL forum posts:

...Google it ...
...RTFM...
...you needs to study...

I instead prefer to discuss technical stuff in forum

I agree with you that "Google it"/"RTFM"/"you needs to study" are useless as standalone responses. But, I explained/discussed the error message before I mentioned search engines, didn't I?

Google and discussions are not mutually exclusive. For example: "I got this error message, 'ABC'. I found this article on Google which says 'DEF' but it doesn't make sense to me because I thought 'XYZ'. Can you please help shed some light on this?" -- this is a good way to start a discussion.

I believe the "no-nos" are pretty given - so why bother to post them?

Some people genuinely don't think of using search engines. I don't make assumptions on what people do or don't know, so I post the recommendation just in case. I believe that quick searches help us to understand the problem better.

Anyway, I've taken note of your personal preferences so I won't bring up Google with you again.