What meaning of the line code with '##'?

Question

Hi,

I read the following GPIO description, but I don't understand the line with '##'. Are there some connection with the above paragraph?

Thanks,

.............................. Accessing such GPIOs requires a context which may sleep, for example a threaded IRQ handler, and those accessors must be used instead of spinlock-safe accessors without the cansleep() name suffix.

Other than the fact that these accessors might sleep, and will work on GPIOs that can't be accessed from hardIRQ handlers, these calls act the same as the spinlock-safe calls.

** IN ADDITION ** calls to setup and configure such GPIOs must be made from contexts which may sleep, since they may need to access the GPIO controller chip too: (These setup calls are usually made from board setup or driver probe/teardown code, so this is an easy constraint.)

gpio_direction_input() gpio_direction_output() gpio_request()

## gpio_request_one() ## gpio_request_array() ## gpio_free_array()

gpio_free() gpio_set_debounce()

Tim Wescott · Accepted Answer

What language?  I don't think a double hash mark would compile in that  context in regular ol' C or C++.  (Inside a #define -- yes.  Outside --  no.) --  Tim Wescott Wescott Design Services

Robert Willy · Answer

It is plain C, for a Linux device driver. I thought whether it was for comment  out, but I don't know what connection with the above paragraph description. Thanks,

Tim Wescott · Answer

Hey wait a minute -- there's no semicolons, either. This looks like some scripting language, not C. --  Tim Wescott Wescott Design Services

Robert Wessel · Answer

As Tim said, this may be inside a macro or something. In any event, we're not seeing something - note that the actual (apparent) function calls don't have a terminator. If those are macro invocations, they'd be OK, but for the token pasting operator to be valid, there would still need to be line continuations.

Are you sure this is *exactly* the code, and all of the relevant context?

Tim · Answer

Probably not C/C++, but ## is the C "token pasting" operator. # starts a  comment in Python (and other languages).

Robert Willy · Answer

I should give the link earlier, excuse me. It is an instruction on GPIO device driver on embedded Linux.

David Brown · Answer

That is a text file, containing a mixture of descriptions and code. You can, I think, assume that this part is just documentation - and that the ## lines are comments (# is a comment character in scripts and many languages).

Tim Wescott · Answer

Indeed.  If it's just stuff interspersed in a web page, then you can't  assume that you can just cut it and paste it into a program file and have  it work. --  Tim Wescott Wescott Design Services

What meaning of the line code with '##'?

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