memmove will never return anything other than dest. Returning dest, as opposed to making memmove void, is useful when the first argument is a computed expression, because it lets you avoid computing the same value upfront, and storing it in a variable. This lets you do in a single line void *dest = memmove(&buf[offset] + … Read more
From the C99 standard (7.21.1/2): 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 … Read more
With memcpy, the destination cannot overlap the source at all. With memmove it can. This means that memmove might be very slightly slower than memcpy, as it cannot make the same assumptions. For example, memcpy might always copy addresses from low to high. If the destination overlaps after the source, this means some addresses will … Read more
I’m not entirely surprised that your example exhibits no strange behaviour. Try copying str1 to str1+2 instead and see what happens then. (May not actually make a difference, depends on compiler/libraries.) In general, memcpy is implemented in a simple (but fast) manner. Simplistically, it just loops over the data (in order), copying from one location … Read more