I am purchasing a comfortable laptop for development but the only operating system available to me is 64-bit (Win7) , now I am basically aware that 64-bit has 8-byte integers and can utilize more RAM, that is about it.
My programming will vary (C++, sometimes PHP) but would like to know:
- Can I build my C++ application to be 32-bit portable (run in a 32-bit computer without needing to build under a 32-bit virtual machine?)
- What are the simple gotchas to watch out for when writing an application (casting, etc)
Processors have been 64 bit for some time. I’m perplexed about why people are afraid to make the move to a 64 bit operating system. A 32 bit OS can’t address much more than 3Gb of RAM, so that’s good enough reason to make the upgrade in my book!
When you’re coding, the biggest difference I’ve encountered to look out for is the size of a pointer!
On a 32-bit compiled program, a pointer is normally 4 bytes. On a 64 bit compiled program, a pointer is normally 8 bytes.
Why does this matter?
Lets say your program uses sockets to communicate a data structure from one process to another. Maybe the server process is 32-bit and the client process is 64 bit.
While the struct might be defined identically in both 32 and 64 bit programs, the 64 bit exe will reserve 8 bytes per pointer (and structures normally contain pointers to other structs as in linked lists etc.).
This can lead to data misalignment when a 32 bit exe communicates a struct to a 64 bit exe.
In (almost?) all cases, communicating pointer values between processes is meaningless anyway, e.g. their data doesn’t matter and can be omitted.
So you might think that communicating pointer values would be an uncommon practise – but the easy way to communicate a struct is to memcpy its contents over a socket, pointers and all!
This is the most significant snag I’ve found so far, when coding 64 bit clients, when our server software is 32-bit.