___________ is a special built-in pointer that is automatically passed as a hidden argument to all nonstatic member functions.

The special built-in pointer that is passed as a hidden argument to all nonstatic member functions of a class is called the "this" pointer.

The "this" pointer is an implicit parameter in all nonstatic member functions of a class. It is a pointer to the object that invokes the member function, and it gives access to the calling object's data members (and sometimes member functions) within the code of the function. The main purpose of the "this" pointer is to allow member functions to access the individual characteristics of each object, which makes the code reusable for multiple objects of the same class.

Here's an example to illustrate the usage of the "this" pointer: ```cpp class Test { int x; public: void setX (int x) { // The 'this' pointer is used to retrieve the object's x member // The local variable 'x' is assigned to the object's x member this->x = x; } void print() { // The 'this' pointer is not necessary here, but it can still be used cout << "x = " << this->x << endl; } }; int main() { Test obj; int x = 42; obj.setX(x); obj.print(); } ``` In this example, the 'setX' member function uses the "this" pointer to set the value of the object's 'x' member to the local variable 'x'. The 'print' function uses the "this" pointer to access the object's 'x' member in the output statement, although it is not strictly necessary.

The "this" pointer is especially crucial when working with operator overloading, where you may need to differentiate between the object for which the member function was called and the other objects involved in the operation. Moreover, it is helpful when you have multiple instances of the same class, and you want each object to act upon its data members. The "this" pointer ensures that the individual object's data can be accessed and acted upon accordingly, instead of accessing a single variable shared among instances.