Storing data in pointers
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Storing data in pointers
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Re: Storing data in pointers
#2I don't want to say you should never do this.
But if you aren't writing a compiler or an embedded system, you should never do this.
Re: Storing data in pointers
#3I don't want to say you should never do this. But if you aren't writing a compiler or an embedded system, you should never do this.
It is also very useful for some lockfree algorithms, e.g. to fit a pointer and a sequence number within a 64-bit value.
Re: Storing data in pointers
#4I don't want to say you should never do this. But if you aren't writing a compiler or an embedded system, you should never do this.
It is also very useful for some lockfree algorithms, e.g. to fit a pointer and a sequence number within a 64-bit value.
You should be very careful when doing that. It may be rare in practice, but it's surprisingly easy to trigger ABA issues with only a 16-bit sequence number.
Re: Storing data in pointers
#5Very old Macs used this trick to squeeze their ROM routines down a bit, operating with 24 bit addressing and using the top bits for flags and whatnot. Of course they ran into trouble when machines with 16MB of memory started appearing. If you do this you might be making more work for yourself in the future when you buy a new machine with 256EB of main memory.
Re: Storing data in pointers
#6The alpha only accessed 8-byte aligned mem addresses (originally anyway). The bottom 3 bits were ignored (masked out) on lookups, per the spec, to allow users to stuff juicy extra info into these.
Re: Storing data in pointers
#7I don't want to say you should never do this. But if you aren't writing a compiler or an embedded system, you should never do this.
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Re: Storing data in pointers
#8This is a nice summary of the practical aspects and considerations. It isn’t something anyone should be doing explicitly on a regular basis but there are occasions, particularly in libraries, where it is the perfect tool for the job.
There is also the inverse use case: smuggling pointers inside status codes, enums, and similar. For example, optionally encoding a pointer to additional error metadata for non-zero result codes. In C++ it isn’t that uncommon to also see Result types implemented similarly when the type allows it.
Re: Storing data in pointers
#9My favorite hack back in MFC days was a combo box which I stored the pointer address in the text (to the right after a lot of spaces so was hidden). When a user chooses an item, parse the pointer and de-reference it back to an object.
Re: Storing data in pointers
#10[deleted]