Adding 64 bit support to existing 32 bit code, is it difficult?

Question

There is a library which I build against different 32-bit platforms. Now, 64-bit architectures must be supported. What are the most general strategies to extend existing 32-bit code to support 64-bit architectures? Should I use #ifdef's or anything else?

Answer 1

The amount of effort involved will depend entirely on how well written the original code is. In the best possible case there will be no effort involved other than re-compiling. In the worst case you will have to spend a lot of time making your code "64 bit clean".

Typical problems are:

• assumptions about sizes of int/long/pointer/etc
• assigning pointers <=> ints
• relying on default argument or function result conversions (i.e. no function prototypes)
• inappropriate printf/scanf format specifiers
• assumptions about size/alignment/padding of structs (particularly in regard to file or network I/O, or interfacing with other APIs, etc)
• inappropriate casts when doing pointer arithmetic with byte offsets