pthread in cpp for different member functions in a class

Question

i started with a simple example http://www.tutorialspoint.com/cplusplus/cpp_multithreading.htm i need to divide in the different cpps and headers i have as the following

class definition in Process_Images.h

void PrintHello(void* threadid);

in Process_Images.cpp

void ProcessImages::PrintHello(void* threadid)
{
   long tid;
   tid = (long)threadid;
   std::cout << "Hello World! Thread ID, " << tid << std::endl;
   pthread_exit(NULL);
}

in the main function

ProcessImages PI;

pthread_t threads[2];
pthread_create(&threads[0],NULL,PI.PrintHello,(void *)i);

the error is -->

/home/nvidia/Desktop/cms/tools/vibrante-vcm30t124-linux/cmsapplication_export/cmsapplication/sampleThread.cpp:333:69: error: cannot convert ���ProcessImages::PrintHello��� from type ���void (ProcessImages::)(void*)��� to type ���void* (*)(void*)���
      pthread_create(&threads[0],NULL,CarDetLEFT.PrintHello,(void *)i);
                                                                     ^

any suggestion please?

No, use C++11 threads instead of pthreads! Seriously, prepare a minimal example and you might find someone to solve this puzzle. — Ulrich Eckhardt
– Ulrich Eckhardt, Commented Dec 7, 2015 at 16:34

SergeyA · Accepted Answer · 2015-12-07 15:33:28Z

1

Since I see C++11 tag in the question, there is absolultey no need to go over pthread route!

std::thread thr(&ProcessImages::PrinteHello, &PI, &i);

will do you good!

answered Dec 7, 2015 at 15:33

SergeyA

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Sander De Dycker · Accepted Answer · 2015-12-07 15:24:08Z

0

Two issues :

the thread function must return void*, not void
the thread function cannot be a (non-static) member function

More details can be found on a reference page for pthread_create.

So, change the return type of ProcessImages::PrintHello to void* and make it static :

class ProcessImages {

  //<SNIP>

  public :
    static void* PrintHello(void* threadid);

  //<SNIP>

};

Then this should work better :

pthread_create(&threads[0], NULL, &ProcessImages::PrintHello, (void*) i);

answered Dec 7, 2015 at 15:24

Sander De Dycker

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2 Comments

user3406305 Over a year ago

i have made it static, and change it void* when i compile i got a linking error undefifined reference to ProcessImages::PrintHello(void+)

Sander De Dycker Over a year ago

@user3406305 : you need to also update the definition of ProcessImages::PrintHello accordingly (in Process_Images.cpp)

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