Expression echo 5? : 1; Why output 5

Is this output null (empty)?

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Is this output null (empty)?

Is the simple notation of the ternary operator, 5 is the true output of 5.

The document has an explanation: ternary operator

An expression (EXPR1)? (EXPR2): (EXPR3) when EXPR1 evaluates to TRUE, the value is EXPR2, and the value is EXPR1 when the EXPR3 evaluates to FALSE.
自 PHP 5.3 起，可以省略三元运算符中间那部分。表达式 expr1 ?: expr3 在 expr1 求值为 TRUE 时返回 expr1，否则返回 expr3。

Since 5 is greater than 0, returning the true,php ternary expression when the second argument is omitted, the result is true, and the first argument is returned.

a ? a : b;//可以缩写为a ?: b;//所以上面句 句子等效为：echo  5 ? 5  : 1 ;

A?: b; , if A is an expression, the expression is not executed again, and a? A:B; If an expression returns ture, it is executed again

Because 5 is true.

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