About a problem encountered by PHP conditional operator and its solution

This article mainly introduces a problem and solution encountered about PHP conditional operators. It has a certain reference value. Now I share it with you. Friends in need can refer to it.

Encountered today Come to a question about the nested use of conditional operators (ternary expressions) in PHP

Phenomena

Let’s first look at a piece of C language code (test.c):

#include<stdio.h>
int main() {
  int x = 1;
  int shit = x == 1 ? 100 : 
     x == 2 ? 200 : 300;
  printf("shit的值:%d\n", shit);
  return 0;
}</stdio.h>

Compile and run it

root$ gcc test.c -o test && ./test
shit的值:100

The answer is as expected, because x==1, so 100 is assigned to shit.

But if we rewrite the above code in PHP (test.php):

<?php $x = 1;
$shit = $x == 1 ? 100 : 
   $x == 2 ? 200 : 300;
echo "shit的值:$shit\n";

Execute it:

root$ php test.php
shit的值:200

We find that it returns The results are different, why is this?

Troubleshooting

First of all, we suspect that it may be a priority issue with comparison operator(==) and conditional operator(?:) in PHP , let’s check the PHP official documentation

##== has a higher priority than ?: (C language This is also true), so

$shit = $x == 1 ? 100 : 
   $x == 2 ? 200 : 300;

$shit = ($x == 1) ? 100 : 
   ($x == 2) ? 200 : 300;

operator combination direction:

This is very similar to the phenomenon described above, The problem should be here. After some research, I got the following conclusion:

• The combination direction of the conditional operator (?:) in C language is

  from right to left, each evaluation starts from the rightmost subexpression, so

int x = 1;

int shit = x == 1 ? 100 : 
     x == 2 ? 200 : 300;
//等效于
int shit = x == 1 ? 100 : 
     (x == 2 ? 200 : 300);
//等效于
int shit = x == 1 ? 100 : 
     (300);// 100

• combination of PHP’s conditional operator (?:) The direction is

  from left to right, and each evaluation starts from the leftmost subexpression, so

$x = 1;
$shit = $x == 1 ? 100 : 
   $x == 2 ? 200 : 300;
//等效于
$shit = ($x == 1 ? 100 : 
   $x == 2) ? 200 : 300;
//等效于
$shit = (100) ? 200 : 300;// 200

is between PHP Conditional operator combination direction, we cannot achieve the effect of if-elseif-elseif-else expression by nesting conditional operators like C/C, unless we add parentheses to the later sub-expressions , in this example it can be solved in this way:

$shit = $x == 1 ? 100 : 
   ($x == 2 ? 200 : 300);

$shit = $x == 1 ? 100 :
     ($x == 2 ? 200 :
     ($x== 3 ? 300 :
     ...
     ($x == 8 ? 800 : 900)))))));

It is recommended that you avoid "stacking" ternary expressions. PHP's
behaviour when using more than one ternary operator within a single statement is non-obvious

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