mempcpy() , then add the terminator yourself to be sure. memcpy has the slightly annoying flaw of returning a copy of the dest argument (already known data) rather than the more useful new information of a pointer to the end of the set memory.
#IFNDEF _GNU_SOURCE
#DEFINE mempcpy(X, Y, Z) (void *)((memcpy(X, Y, Z) - 1) + Z)
#ENDIF // Not quite the same but close enough mempcpy, fails for Z = 0
edited: Since X shouldn't be NULL and thus not 0, apply the subtraction first to avoid the corner case (which also shouldn't happen given common HW / OS regions) of X + Z > (~(size_t)0) (SIZE_MAX)
I remembered the return value incorrectly. It's even better in that it returns a pointer to the byte immediately AFTER the last written. So remove the - 1. PS: there's also a version which works with wchar_t types (be it 2, 4 or whatever else)
#DEFINE mempcpy(X, Y, Z) (void *)(memcpy(X, Y, Z) + Z)
#DEFINE wmempcpy(X, Y, Z) (void *)(memcpy(X, Y, Z * sizeof(wchar_t)) + Z * sizeof(wchar_t))
