Difference between %d and %p printf format string directives in c language?

Question

I want to get a detailed explanation on the difference between using %d and %p type for printing pointer.

Also Why does %p return hexadecimal? What are the cases when %d and %p return different values? Does datatype only represent the way the user wants the output or it has something to do with the memory locations too?

Answer 1

For the program to be well-defined, the format specifier must match the type of the argument. Therefore you can use %p but not %d to print out pointers. (The latter might happen to work on some architectures but is technically undefined behaviour.)

The primary reason you can't freely interchange %d and %p is that ints and pointers don't have to have the same size.

The format in which pointers are printed out is architecture-specific (pointers can have different size or indeed different structure). It is, however, common to transcribe memory addresses in hexadecimal, so this is what %p usually does.