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> C99 specifies that it is fine to pass zero to memcpy as the size parameter. 7.24.1(2): Where an argument declared as size_t n specifies the length of the array for a function, n can have the value zero on a call to that function. Unless explicitly stated otherwise in the description of a particular function in this subclause, pointer arguments on such a call shall still have valid values, as described in 7.1.4. On such a call, a function that locates a character finds no occurrence, a function that compares two character sequences returns zero, and a function that copies characters copies zero characters. My question wasn't about passing zero as the size/length, it was about acceptable values for the associated memory pointers when the size was zero. On two different occasions I’ve had C runtimes that have faulted when passed a NULL pointer
to (say) memcpy when the length was zero. I agree that this is not in accordance with standards, nor is it particularly sensible, but I wanted clarity on how Lua handled such a situation (since the specs are silent on this). Pointers must be always non zero for memcmp. See for example [1] which has the relevant std-references. Another point is that compilers start to optimize away null-pointer checks when this pointer was used in memcmp. [2] - Jörg [1]
http://stackoverflow.com/questions/16362925/can-i-pass-a-null-pointer-to-memcmp [2]
https://gcc.gnu.org/ml/gcc-patches/2015-05/msg02707.html |