linux - What does a double underscore mean in a variable name in the C language? -

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possible duplicate:
why people use __(double underscore) in c++

i studying linux kernel programming code.

there data structures , functions start double underscore like:

__u32  len

how different normal variables?

it means it's system-reserved name. c standard says names beginning 2 underscore, or underscore , capital letter, reserved use of system or compiler , should not defined in application code.


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