php三元运算符格式化

Question

This works:

<input type="text" name="foo" value="<?php echo isset($_POST['foo']) ? $_POST['foo'] : '' ?>"/>

This does not:

echo('<input type="text" name="foo" value="'.isset($_POST['foo']) ? $_POST['foo'] : ''.'"/>');

Notice: Undefined index: foo in /srv/www/form.php on line 15

Thanks for any help.

Answer 1

PHP's operator precedence rules make it evaluate your second example as follows:

echo(
  ('<input type="text" name="foo" value="'.isset($_POST['foo']))
    ? $_POST['foo']
    : (''.'"/>')
);

That doesn't make a lot of sense in several ways. And since the result of isset() is essentially disregarded, this always ends up just trying to print $_POST['foo']. And that results in a notice when it's not set, of course.

Add parentheses around the actual ternary expression. I.e.

(isset($_POST['foo']) ? $_POST['foo'] : '')