C / C++ / MFC

4-Sep-22 21:37

Member 14968771 wrote:
The att6ached code is being posted here because
it is C++ code

No, it has nothing to do with C++, it is purely a QT/qterminal issue. And this is the C/C++ forum.

In your code ...

C++

QString exec = "qterminal";

QStringList params = QStringList() << "qterminal" << "-e" << "bluetoothctl" ; // help\n";
processTERMINAL->start(exec, params);

... you are passing "qterminal" as the first parameter to "qterminal". So remove that field from your params.

And that is still not a C++ issue.

modified 5-Sep-22 4:30am.

Message Closed

29-Aug-22 7:23

Member 14968771

29-Aug-22 7:23

Message Closed

modified 15-May-23 19:06pm.

Victor Nijegorodov29-Aug-22 7:40

Victor Nijegorodov

29-Aug-22 7:40

Did you try to compare your these two "usages" to see the difference between them?

Maximilien29-Aug-22 8:23

Maximilien

29-Aug-22 8:23

I'm no QT expert, so YMMV.

You could probably just iterate the QString as an array?

see : https://stackoverflow.com/questions/18916099/search-qstring-character-by-character

CI/CD = Continuous Impediment/Continuous Despair

CPallini29-Aug-22 20:05

CPallini

29-Aug-22 20:05

Quote:
1. I thought 'foreach" was a C++ "feature" - in QT doc they call it macro "Q_FOREACH" -
not sure which way is up...

Then you were wrong. C++ has NO foreach construct, however, it provides the range-based for, see Range-based for loop (since C++11) - cppreference.com[^].

Quote:
2. The syntax
foreach(QString str, StringArray[MAX_ARRAY])

I cannot find the StringArray class in QT documentation. Do you meant QStringList Class | Qt Core 6.3.2[^]?
On the other hand, if you use a (C-like) array of QStrings, then you could use the C++ range-based for.

"In testa che avete, Signor di Ceprano?"
-- Rigoletto

Message Closed

30-Aug-22 3:11

Member 14968771

30-Aug-22 3:11

Message Closed

modified 15-May-23 19:06pm.

CPallini30-Aug-22 3:16

CPallini

30-Aug-22 3:16

You are welcome.

"In testa che avete, Signor di Ceprano?"
-- Rigoletto

Richard MacCutchan29-Aug-22 21:56

29-Aug-22 21:56

QString offers a standard C++ iterator: QString Class | Qt Core 6.3.2[^]. So (assuming qstr is the reference to your string) you can try something like:

C++

for (QString::iterator it = qstr->begin(); it != qstr->end(); ++it)
{
    // it now points to each character in turn
}

linker error lnk2005

Roberto64_Ge29-Aug-22 4:19

29-Aug-22 4:19

I am dealing with a school exercise in c++ within an Ubuntu virtual machine. I have a header.h with the class, a header.cpp with the method implementation, a main.cpp and i compile it (main.cpp includes header.cpp which includes header.h) with the following: g++ main.cpp -Wall -o main (from ubuntu terminal). Then I run it and that's ok.
I then tried to import the same exercise in visual studio 2019 creating at first an empty c++ project. After I tried with a CMake project. In both cases compiler/linker return error LNK2005 relevant to all the method implementation saying that they are already defined in main.cpp.obj.
I would attach the complete project in both versions (Ubuntu side and vstudio19 side) but I do not see how. Regards

k505429-Aug-22 4:35

k5054

29-Aug-22 4:35

Roberto64_Ge wrote:
main.cpp includes header.cpp which includes header.h

This is probably the source of your problem. Visual Studio is probably compiling header.cpp and creating a separate object file, then compiles main.cpp, which includes header.cpp, and so creates two copies of the methods defined in header.cpp. In general it is a mistake to #include a cpp file in another cpp file. You main.cpp only needs to include header.h, which should only provide a declaration of your class. You would then compile main.cpp and header.cpp separately.

You can do this on the ubuntu command line using

g++ -Wall -Wextra main.cpp header.cpp -o main

or alternatively

g++ -Wall -Wextra -c main.cpp
g++ -Wall -Wextra -c header.cpp
g++ main.o header.o -o main

In the above example, the -c option to g++ tells the compiler to only produce an intermediate object file (e.g. a .o file), and not try to produce an executable. The third line creates the final executable, and includes all the system libraries and startup code needed for the executable.

Keep Calm and Carry On

Roberto64_Ge29-Aug-22 5:03

29-Aug-22 5:03

Thank you, your answer is clear. Now the point is that I am not used at all in c++ compiling/linking and I am not used to VS configuration of compiler and linker, so I ask if you could help. Correct me if I am wrong : (we are within VS2019)
1) a create a new cc++ emty project
2) Add main.cpp , header.cpp and header.h to the project.
3) Include header.h in main.cpp
Now from the VS2019 environment, how do I compile separately main.cpp and header.cpp? I guess I have to compile header.cpp before. Isn't it? But how do I do that?
And then, how do I compile main.cpp and how the VS2019 knows, while compiling main.cpp, where to get the method implementation i.e. the header.obj?

k505429-Aug-22 5:09

k5054

29-Aug-22 5:09

If you've created a VS C++ project, it knows how to deal with files that you add to the project. All you should need to do for a simple project is hit Build, and the IDE will take care of the rest.

Keep Calm and Carry On

Roberto64_Ge29-Aug-22 5:13

29-Aug-22 5:13

Ok I tried and I did it. I right clicked on header.cpp and it gave the option to compile. This created the header.obj. Then I right clicked on the main.cpp and again I had the option to compile it and this generated the exe. Before doing all this I included in the main.cpp only header.h,
Now it works. Thanks for the clear explanation

k505429-Aug-22 5:28

k5054

29-Aug-22 5:28

That's one way to do it, but not the most efficient: Building and Cleaning Projects and Solutions - Visual Studio (Windows) | Microsoft Docs

Keep Calm and Carry On

Roberto64_Ge29-Aug-22 8:56

29-Aug-22 8:56

ok i will read it
Thumbs Up | :thumbsup:

Richard MacCutchan29-Aug-22 4:45

29-Aug-22 4:45

Roberto64_Ge wrote:
main.cpp includes header.cpp which includes header.h

This means that all the definitions in header.cpp will be duplicated in the object files. Do not include .cpp files in others, only include the actual headers, i.e. in this case main.cpp should only include header.h.

Roberto64_Ge29-Aug-22 5:14

tracking down linker errors

29-Aug-22 5:14

ok thanks

Calin Negru27-Aug-22 3:50

Calin Negru

27-Aug-22 3:50

I there a way to track down the linker errors further than what`s being offered in the "Build output" window?

Re: tracking down linker errors

Mircea Neacsu27-Aug-22 4:03

Mircea Neacsu

27-Aug-22 4:03

Not really. You can increase number of linker messages by changing the "Show Progress" option. The "Display all messages" is really verbose.

Otherwise, sometimes they can be tricky to trace. Just yesterday I had one where an include directive was used after a

C++

namespace blah_blah {

line. Linker was looking for a function definition inside the namespace when it was actually outside.

Mircea

Re: tracking down linker errors

Richard MacCutchan27-Aug-22 6:44