This routine uses the values specified in the stackaddr and size arguments to set the base stack address and size of the thread attributes object specified in the attr argument. When creating a thread, use a thread attributes object to specify nondefault values for thread attributes. The default value for the stack address attribute of an initialized thread attributes object is NULL. Unlike pthread_attr_setstackaddr(), this routine is a much more reliable portable interface. With the POSIX standard pthread_ attr_setstackaddr(), a stack is specified using a single, undefined, address. An implementation of the standard can only assume that the specified value represents the value to which the thread's stack pointer should be set when beginning execution. However, this requires the application to know how the machine uses the stack. For example, a stack may "grow" either up (to higher addresses) or down (to lower addresses), and may be decreased (or increased) either before or after storing a new value. The Threads Library provides an alternative interface with pthread_attr_setstackaddr_np(). Instead of specifying a stack address, you specify the base (lowest) address and the size.