> > On Sat, Jan 2, 2010 at 8:10 AM, Shawn <[email protected]> wrote: >> >> hello guys, >> I got a newbie confused when I was looking into the source code of >> s3c2440's RTC driver.I dont know what is __v excatly means.anyone can >> tell?thanks anyway! >> >> #define readb(c) ({ __u8 __v = __raw_readb(__mem_pci(c)); __v; })
On Sun, Jan 3, 2010 at 11:49 AM, Anand Arumugam <[email protected]> wrote: > I think the last __v; inside the macro is to avoid compiler warning or error > that the unsigned 8-bit variable __v is not being used inside the scope > defined by the macro. No, I believe it is the value assigned to the statement sequence wrapped in the {} pair. ie. {statement1; statement2; variable} evaluates to the value of the variable which is the last statement. Thus c code with: ret = readb(c); will assign ret to __v which in turn is the value returned from __raw_readb(). Thus the above macro structure is the standard way to return a value from a macro. You will find similar macro usage throughout the kernel. Greg -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to [email protected] Please read the FAQ at http://kernelnewbies.org/FAQ
