Are All Pointers the Same Size in C ?

Do All Pointers Have the Same Size in C ?

The question arises whether all pointers in C share a uniform size. While it's often assumed, the C standard provides definitive insights into this matter.

C Standard Specifications

The C standard explicitly guarantees:

• void and char are of equal size (section [basic.compound]/5).
• Pointers to different cv-qualified versions of the same type (T const, T volatile, and T const volatile*) share the same size ([basic.compound]/3).
• Pointers to enum types with identical underlying types have the same size (section [dcl.enum]/9).

Practical Considerations

In practice, pointers to class types generally maintain identical sizes. This is due to the requirement that the compiler must determine the size of T* without fully defining T. While compilers have some flexibility in pointer sizing, this is rarely exercised in real-world scenarios.

Additionally, function pointers, pointers to data members, and pointers to function members typically have the same size. This allows for seamless reinterpret_casting between these pointer types.

Exceptions

One notable exception occurs in segmented architectures, where near and far pointers may differ in size. This case defies the usual rules for pointer size uniformity.

Conclusion

The C standard clarifies that void* and cv-qualified pointers have a uniform size. While pointers to different types generally inherit the same size, practical considerations suggest that pointers to class types, function pointers, and pointers to data members all share a unified size. However, segmented architectures present an exception, with near and far pointers potentially having different sizes.

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