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What does this line of code mean?

I was reading an article on Opencv, and came across this:

for( i = 0; i < (faces ? faces->total : 0); i++ ) 
{
    CvRect* r = (CvRect*)cvGetSeqElem(faces, i);
}

What in the world is this line supposed to mean:

i < (faces ? faces->total : 0)

Answer 1

It’s the conditional operator.

The (faces ? faces->total : 0) tests faces. If it’s true, then faces->total is returned and compared with i. Otherwise, if it evaluates to false, i is compared to 0.