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64-bit memory alignment

chsalvia
chsalvia asked
on
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Last Modified: 2008-02-01
Suppose you store a 64-bit value in memory, at an address that is not divisible by 8, but is divisible by 4.

For example:

char buf[100];
uint64_t num = BIGNUMBER;
memcpy(buf + 4, &num, sizeof(num));
printf("%lld\n", *((uint64_t*) (buf+4)));

This is no problem on a 32-bit system, but is there any danger in doing this on a 64-bit system?  I tested this on a 64-bit system running Linux and it worked fine.  But I'm wary of memory alignment issues that result from porting to 64-bit.
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