Call a function in Shared Library on Linux

I created a shared library written in C/C++. How do I a call a function in the shared library from PHP ?

Functions in shared library:
1.
void SetCurrentPos(int pos)
{
}

2.
int GetCurrentPos()
{
     return m_Pos;
}

Could anyone show me a simple example of how I could call the above function in PHP ? Thanks.