Function prototype with ellipsis [duplicate]

Question

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• what is the use of … in c++ 2 answers

I was wondering if the below function prototype is valid. It compiled fine, but the three period is kinda throwing me off and I couldn't find anything similar on Google.

void foo(int, ...);

Thanks!

Answer 1

Yes, it's valid. In this example, ... creates a variadic function using the va_list mechanism. This is how variadic functions are implemented in C, and to some degree in C++ (though C++11's template parameter packs have rendered this mechanism obsolete).

Further reading: va_arg