What is the maximum size of buffers memcpy/memset etc. can handle?

Question

What is the maximum size of buffers memcpy and other functions can handle? Is this implementation dependent? Is this restricted by the size(size_t) passed in as an argument?

Answer 1

There is also an issue related to what size_t can represent verses what your platform will allow a process to actually address.

Even with virtual memory on a 64-bit platform, you are unlikely to be able to call memcpy() with sizes of more than a few TB or so this week, and even then that is a pretty hot machine.... it is hard to imagine what a machine on which it would be possible to install a fully covered 64-bit address space would look like.

Never mind the embedded systems with only a few KB of total writable memory, where it can't make sense to attempt to memcpy() more information than the RAM regardless of the definition of size_t. Do think about what just happened to the stack holding the return address from that call if you did?

Or systems where the virtual address space seen by a process is smaller than the physical memory installed. This is actually the case with a Win32 process running on a Win64 platform, for example. (I first encountered this under the time sharing OS TSX-11 running on a PDP-11 with 4MB of physical memory, and 64KB virtual address in each process. 4MB of RAM was a lot of memory then, and the IBM PC didn't exist yet.)