Question

What are the points that should be kept in mind while writing code that should be portable on both 32 bit and 64 bit machines?

Thinking more on this, I feel if you can add your experience interms of issues faced, that would help.

Adding further on this, I once faced a problem due to a missing prototype for a function which was returning returning a pointer. When I ported the same to a 64 bit machine, the code was crashing and I had no clue about the reason for quite some time, later realised that all missing prototypes are assumed to return int causing the problem.

Any such examples can help.

EDIT: Adding to community wiki.

Answer 1

Gotchas:

1. Casting pointers to integer types is dangerous
2. Data structure sizes can change
3. Watch out for sign extension
4. Different ABI?

Some tips & tricks I’ve found helpful:

1. Get yourself a native-size integer type (from a header or typedef your own) and use it when you have variables that don’t care about size.
2. Use explicit variable types wherever possible (u_int64_t, int_32_t, etc.)