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Possible Duplicate:
Why do people use __(double underscore) so much in C++
I was studying the Linux kernel programming code.
There are some data structures and functions which start with a double underscore like:
__u32 len
How is that different from normal variables?
It means it’s a system-reserved name. The C standard says that all names beginning with two underscore, or underscore and capital letter, are reserved for the use of the system or compiler and should not be defined in application code.