Question

How do I determine whether the currently running Mac OS X system is of 32bit or 64bit machine?

Answer 1

It depends on what you mean by "64 bit machine". There are broadly three categories depending on processor family:

Supports some 64-bit math operations
Can run programs in X-64 mode (64-bit addressing)
Has 64-bit kernel support

I assume that you mean sense "2" here, since that s the most relevant for application code. You don t have to worry about sense "1" unless you need to run on older PowerPC Macs, I believe.

You specifically mentioned doing this in C code, which doesn t actually make much sense. If you re compiling C code, you can just build your application "fat", with 32- and 64- bit variants, and therefore do the check at compile-time with:

#if _LP64
//64-bit stuff
#else
//32-bit stuff
#endif

Answer 2

I m fairly certain that sizeof(long) == 4 on 32-bit systems and sizeof(long) == 8 on 64-bit systems. The same should be true of pointers.

Answer 3

a little greppy, but ..

#!/bin/sh

ioreg -l -p IODeviceTree | grep EFI64
if [ $? = 0 ]
then
    echo "I am a 64bit machine!"
else 
    echo "I am a 32bit machine!"
fi

wrapped in an NSTask *task = [[NSTask alloc] init]; ...?

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