For example, this program uses stpcpy to concatenate foo and bar to produce foobar, which it then prints.
char *to = buffer;
to = stpcpy (to, "foo");
to = stpcpy (to, "bar");
printf ("%s\n", buffer);
This function is not part of the ANSI or POSIX standards, and is not customary on Unix systems, but is not a GNU invention either. Perhaps it comes from MS-DOS.
strcpy(3), bcopy(3), memccpy(3), memcpy(3), memmove(3)