c++ - 三元运算符 a = b ?: c 是什么意思

Question

注意：我很清楚 a = b ? c : d 是什么意思，可这不是我要问的问题。

三元运算符 a = b ?: c 是什么意思。注意， ?和: 是在一起的

Answer 1

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Answer 2

a = b ?: c is the abbreviation of a = b ? b : c.

Answer 3

b = true
c = false
a = b ?: c  // a = true

b = false
c = true
a = b ?: c // a = true

Answer 4

Although the title of the question is tagged C and C++, I wrote a PHP script to test it, and the results are as follows:

php<?php
$b = true;
$c = false;
$a = $b ?: $c;
var_dump($a); // 输出true

$b = false;
$c = true;
$a = $b ?: $c;
var_dump($a); // 输出true

From the output result, the meaning of a = b ?: c is: if b is true, then a = b, if b is false, then a = c

Answer 5

The format should be

(boolean expression) ? a : b

If the content of the boolean expression is true, then a.
If the content of the boolean expression is false, then b.

For example:

javapublic int test(int a) {
    if (a > 0) {
        return 1;
    } else {
        return -1;
    }
}

The above if-else can be replaced by ternary operation, as follows:

java    public int test(int a) {
        return (a > 0) ? 1 : -1;
    }