Windows SDK Thread: How to use member functions as thread functions?
Sat, 24/02/2007 - 10:25 — admin
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Q: How to use member functions as thread functions?
A: While trying to use member functions of a class as thread functions the compiler might complain with some kind of error like
error C2664: 'CreateThread' : cannot convert parameter 3 from 'unsigned long (void *)' to
'unsigned long (__stdcall *)(void *)'
None of the functions with this name in scope match the target type
'unsigned long (__stdcall *)(void *)'
None of the functions with this name in scope match the target type
or
error C2665: 'AfxBeginThread' : none of the 2 overloads can convert parameter 1 from
type 'unsigned int (void *)'
The problem is that every thread function has its own prototype, which determines the parameters that gets passed from the operating system to it.
In C++ every member function has a hidden parameter - the so-called 'this' pointer which will be automatically passed to the function. C++ is able to associate a function with a particular instance of an object by means of the 'this' pointer. Member functions access member variables through the 'this' pointer...
class foo
{
public:
void func() { integer_ = 0; }
private:
int integer_;
};
{
public:
void func() { integer_ = 0; }
private:
int integer_;
};
This code will be compiled as
class foo
{
public:
void func(foo* this) { this->integer_ = 0; }
private:
int integer_;
};
{
public:
void func(foo* this) { this->integer_ = 0; }
private:
int integer_;
};
The operating system does not call thread functions through objects therefore it cannot handle the automatically added 'this' pointer... To get member functions working as thread routines you need to tell the compiler explicitly not to expect a 'this' pointer. To avoid the automatic 'this' pointer you have two possibilities:
- Non-member functions
- Static member functions
Non-member functions are not part of a class and therefore do not have a 'this' pointer. Static member functions do not receive a this' pointer either...thus, if you want to use a member function as a thread routine you need to declare it as 'static'...
More information can be found here and here.
Note: Most of the material in this article is taken from codeguru.com
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