Re: Using function pointers in c++

Ian Collins <>
Thu, 22 Feb 2007 07:47:28 +1300
<> wrote:


I have had this problem several times before, and each time I have
been turned back forced to find another way. But not this time...

How can you cast a Class::* into a void *.

For this example I am using pthread and to start a thread you need to
pass it a void* (*)(void*)

however I have the run function inside a class:

class ThreadBase {
  ThreadBase() {}
  virtual void run() = 0;
 void start_thread(){pthread_create( &__thread_id, 0, this->run, 0 );}

You just can't do this. The pthread_create function expects a C
function of the form void* (*)(void*). Any class member function will
have a hidden this parameter, which isn't a void*. A class member
function has C++ linkage.

The only correct form is to declare a function extern "C" and pass that
function to pthread_create.

extern "C" void start( void* );

void start( void *p )
  ThreadBase *base = static_cast<ThreadBase*>(p);

Ian Collins.

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