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Editorial Team
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Asked: 2026-05-28T19:24:17+00:00

I have been looking through some MFC code and i came across this expression.

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I have been looking through some MFC code and i came across this expression. It was in OnInitDialog() function, didn’t look like it’s MFC specific. The variables had some name, value was 0.

int volatile something, somethingElse; //this was global

something, somethingElse = 0; //this was inside the function

Does this make any sense in C++? I know how the comma operator works, though in a free form like here it should be separating expressions. Is a variable name also an expression? This code does compile, so how does this work?

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1 Answer

  1. Editorial Team

    This is likely an error in the program. The statement

    a, b = c;

    Is completely equivalent to

    b = c;

    Since the comma operator evaluates from left to right and discards all values except the last. Since the expression a has no side effects, it’s essentially a no-op.

    I would suspect that this is either programmer error or an incorrect translation of code from a different language into C++. You should contact the author to let them know about this.

    Hope this helps!

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