What is "..." and "##"

Code:

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#define INFO(fmt, args...) { SYS_INFO( fmt, ## args ); }

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What is "..." and "##" here?

Here's gcc's documentation on it: http://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html

gg

Keep in mind it is not standard C or C++. It is an extension specific to gcc.

## is in 6.10.3.3 in ISO/IEC 9899:TC2.

... is also in there spread around.

You're correct that ## is in the C standards and the C++ standard as a preprocessor directive for token pasting, rob. However, the usage above, which is concerned with defining macros with variable argument lists, is specific to gcc.