looks like I'm a bit overstrained with this answer as an Arduino beginner
May be its better to use the uint32_t unixtime() function- but this seamst to be not in the library I'm using.
Where can I Download the right library ?
when you do a = (clock.dateFormat("U", dt); besides missing a parenthesis and not looking at the compiler warnings, what you do is store in your a variable the address of the pointer to the char buffer.
There is another function returning the unix time in your library
[color=green][b]uint32_t[/b][/color] unixtime()
note that it returns an unsigned long on 32 bits, not a long