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.

Use of uintptr_t for casting is usually safer than intptr_t, especially for comparisons.