What’s the difference between %p and %x when printing pointers in C?

Although a pointer is represented like a number at the machine level, C does not treat pointers and integers as the same type. On many common computers, %x may appear to work for an address, but that is only accidental and is not portable C. The correct approach is %p for a pointer and %x for an integer value that you intentionally want shown in hexadecimal.

In an expression like printf("%pn", (void*)&x), the & operator obtains the address of x, and %p formats that pointer for display. Printing an address is mostly useful for learning, debugging, or inspecting how pointers work; ordinary programs usually don’t need to display addresses directly.

%p tells printf that the argument is a pointer, while %x tells it to expect an unsigned integer and display that integer in hexadecimal. Even if they produce similar-looking output on many systems, they are not interchangeable. Use %p for pointers, typically by casting the pointer to void*, such as printf("%pn", (void*)&x). Use %x when you actually want to print an integer in hexadecimal. Because printf is variadic, it relies on the format string to interpret each argument correctly, and using the wrong specifier can cause undefined behavior or fail on systems where integers and pointers have different representations.