Pointer to Pointer

A pointer to a pointer, also known as a double pointer, is a form of multiple indirection in C. Just as a regular pointer stores the address of a variable, a double pointer stores the address of another pointer variable. This creates a chain of pointers, allowing for more complex data manipulation and memory management. You declare a double pointer by adding a second asterisk before its name. For example, `int **p2p;` declares `p2p` as a pointer to a pointer to an `int`. Let's break down the levels. You might have a regular integer variable, `int var = 10;`. A normal pointer, `int *p1 = &var;`, stores the address of `var`. Then, a double pointer, `int **p2p = &p1;`, can store the address of the pointer `p1`. To access the final value (`var`) through the double pointer, you need to dereference it twice. `*p2p` would give you the value of `p1` (which is the address of `var`), and `**p2p` would give you the value of `var` itself (which is 10). Double pointers are not just an academic concept; they have practical applications. They are commonly used when you want a function to modify a pointer that was passed to it. Since C passes arguments by value, passing a regular pointer only allows the function to modify the data the pointer points to, not the pointer itself. By passing a pointer to that pointer, the function can change the original pointer in the calling scope. They are also frequently used for creating and managing dynamic two-dimensional arrays.