在这段PHP代码中，“？”和“：”是什么意思？ [重复]

Question

This question already has an answer here:

• What is the meaning of the '?', '()', and ':' symbols in PHP? 4 answers

I'm trying to convert this PHP function to Objective-C. I can just barely read PHP to figure out what the code does. Came across this line and stopped:

$nr = (strlen($nr)-3>0)?substr($nr, 0, strlen($nr)-3):"";

What do the ? and : do here? I read the documentation to see what strlen and substr do but haven't been able to figure out how this comes together and what the new value of $nr is.

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Answer 1

The ?: is a ternary operator. The expression x ? y : z means if x then y else z. In this case, it would translate to something like

if strlen($nr) - 3 > 0:
    $nr = substr($nr, 0, strlen($nr) - 3)
else:
    $nr = ''