Yes, you are definitely correct, that is what the standard specifies. However, many programmers assume that if the source string points to a higher memory location than the destination string, then it is ok (i.e., they want to shift a string of X bytes to the left by some amount). And they've gotten away with it for many years, because most strcpy() functions are implemented very simply (they copy one byte at a time). The problem is when 15 year old code is run on a newer platform that has an SSE4 optimized implementation of strcpy -- then they find out what is meant by "undefined behavior".