uintptr_t and Other Helpful Types

Other useful types provided by <inttypes.h> include signed and unsigned integer types large enough to hold a pointer. These are given as intptr_t and uintptr_t. In addition, intmax_t and uintmax_t are defined to be the longest (in bits) signed and unsigned integer types available.

Using the uintptr_t type as the integral type for pointers is a better option than using a fundamental type such as unsigned long. Even though an unsigned long is the same size as a pointer in both the ILP32 and LP64 data models, the use of the uintptr_t requires only the definition of uintptr_t to change when a different data model is used. This makes it portable to many other systems. It is also a clearer way to express your intentions in C.

The intptr_t and uintptr_t types are extremely useful for casting pointers when you want to do address arithmetic. They should be used instead of long or unsigned long for this purpose.