The man page for strcpy:
You need both source and destination when using strcpy()
strcpy, strncpy - copy a string
char *strcpy(char *dest, const char *src);
char *strncpy(char *dest, const char *src, size_t n);
The strcpy() function copies the string pointed to by src (including
the terminating `\0' character) to the array pointed to by dest. The
strings may not overlap, and the destination string dest must be large
enough to receive the copy.
The strncpy() function is similar, except that not more than n bytes of
src are copied. Thus, if there is no null byte among the first n bytes
of src, the result will not be null-terminated.
In the case where the length of src is less than that of n, the remain-
der of dest will be padded with nulls.
The strcpy() and strncpy() functions return a pointer to the destina-
tion string dest.
If the destination string of a strcpy() is not large enough (that is,
if the programmer was stupid/lazy, and failed to check the size before
copying) then anything might happen. Overflowing fixed length strings
is a favourite cracker technique.