c++ - Why this code compiles in VS? ("extra" comma) -

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the line below inside loop. if method fails, needs break. category_1 enum. added enum new parameter addtolist method default value. if see closely below, made mistake of putting comma , enum outside parameter list of function. compiles fine vs2010. had hard time finding that default value being passed parameter instead of category_1. know why succeeds?

if (! addtolist(obj1, (unsigned int) val), category_1) {     break; }

in c++, comma isn't separator; can operator. comma operator. comma operator evaluates first expression, discards result, evaluates second expression , yields result.

!addtolist(obj1, (unsigned int) val) , category_1 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   ^^^^^^^^^^ first expression                       second expression

[of course, comma operator, other operators, can overloaded, , if overload used here, semantics different. behavior of built-in comma operator.]


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