[ale] OT: dummy C++/threads question

[John Mills]

Christopher, ALErs -

On Wed, 23 Jul 2003, Christopher Fowler wrote:

> Remove the '&' and that should pass the function through.  What
> are the errors you are getting?

Declaration of member to be started:

void * CCamera::RunOneCamera(void * lpParam)
{ blah }

Function to start the thread:
...
  idCThread = pthread_create(&(cThread[Ci]), NULL,
			     CCamera::RunOneCamera,  &cParm[Ci]);
...

Compiler (g++) says:

...
Camera.cpp: In method `int CCamera::ServeACamera (int)':
Camera.cpp:165: assuming & on `CCamera::RunOneCamera'
Camera.cpp:165: cannot convert `void *(CCamera::*) (void *)' to `void 
*(*) (void *)' for argument `3' to `pthread_create (pthread_t *, const 
pthread_attr_t *, void *(*) (void *), void *)'
...

If I put in the '&' it still refuses the type on the same basis.

If I make 'void *RunOneCamera(void*)' a local function instead of a class
member (and drop it from the member list in Camera.h), the argument is
passed successfully - with or without the '&' (which I think _is_ needed).
Stroustrup(2nd ed) gives an example (5.4.5, pg.166), but I can't seem to
get it together.

Thanks for any ideas.

> > I have a C++ class with a member function, say:
> > 
> > void * CMyClass::MyFunction(void * myArgs) {blah}
> > 
> > I want to this function to be executed in a thread started by another 
> > member of the same class:
> > 
> > fnType CMyClass::MyManager()
> > {
> >   ...
> >   pthread_create(&someInt, NULL, &CMyclass::MyFunction, &someStruct);
> >   // can't get this right-->>    ^^^^^^^^^^^^^^^^^^^^^
> > }

 John Mills
 john.m.mills at alum.mit.edu

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