将 echo 和 print 组合在一个语句中 [英] Combine an echo and a print in one statement

问题描述

echo "1" .(print '2') + 3; 返回 214. 脚本如何以 *14 结尾?

echo "1" . (print '2') + 3; returns 214. How does the script end up with *14?

推荐答案

什么时候做

echo "1" . (print '2') + 3;

PHP 会做(演示)

line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
   2     0  >   PRINT                                            ~0      '2'
         1      CONCAT                                           ~1      '1', ~0
         2      ADD                                              ~2      ~1, 3
         3      ECHO                                                     ~2
         4    > RETURN                                                   1

一句话:

• 打印2，返回1
• 连接1"并返回 1 =>11"
• 添加11"+ 3 => 14
• 回声 14

那是 214.

运算符 + - . 具有相同的 运算符优先级，但保持关联:

The operators + - . have equal Operator Precedence, but are left associative:

对于优先级相等的运算符，左结合性表示求值从左到右进行，而右结合性则相反.

For operators of equal precedence, left associativity means that evaluation proceeds from left to right, and right associativity means the opposite.

<小时>

因为所有其他答案都声称 PHP 是 1+3，这里进一步证明它不是:

---

since all the other answers claim PHP does 1+3, here is further proof that it doesnt:

echo "1" . (print '2') + 9;

给出 220，例如11+9 而不是 1 .(1+9).如果加法优先于串联，则为 2110，但为此您必须编写

gives 220, e.g. 11+9 and not 1 . (1+9). If the addition had precedence over the concatenation, it would have been 2110, but for that you'd had to write

echo "1" . ((print '2') + 9);

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