How to use QtConcurrent::functions and what is my error?

[CuriousPan]

Hello everyone!
I have a list of strings and I want to process them in parallel performing some actions on them. However, when I try to build my code, I have an error stating that the desired function cannot be called. What is my problem?

Here's the code I'd like to run:

QStringList filePaths;

QString Controller::action(QString& str)
{
    // make some actions on files
    return str; // I don't really care about the return value.
}

QtConcurrent::map(filePaths, &Controller::action);

When I try to build my code I get a following error:

C:\Qt\5.15.2\mingw81_64\include\QtConcurrent\qtconcurrentmap.h:49: In file included from C:/Qt/5.15.2/mingw81_64/include/QtConcurrent/qtconcurrentmap.h:49,
In file included from C:/Qt/5.15.2/mingw81_64/include/QtConcurrent/qtconcurrentmap.h:49,
                 from C:/Qt/5.15.2/mingw81_64/include/QtConcurrent/QtConcurrentMap:1,
                 from C:/copyrightadder/src/Controllers/Controller.cpp:10:
C:/Qt/5.15.2/mingw81_64/include/QtConcurrent/qtconcurrentfunctionwrappers.h:132:14: note: candidate: 'T QtConcurrent::MemberFunctionWrapper1<T, C, U>::operator()(C&, U) [with T = QString; C = Controller; U = QString&]'
     inline T operator()(C &c, U u)
              ^~~~~~~~
C:/Qt/5.15.2/mingw81_64/include/QtConcurrent/qtconcurrentfunctionwrappers.h:132:14: note:   candidate expects 2 arguments, 1 provided

[SGaist]

Hi,

If you want to use a member function, the array you pass to the map method must contain items of that class.