is_string

(PHP 4, PHP 5, PHP 7, PHP 8)

is_string — 检测变量是否是字符串

描述

is_string(mixed $var): bool

如果 var 是 string 则返回 true，否则返回 false。

参见 is_bool()、is_int()、is_integer()、is_float()、is_real()、is_object() 和 is_array()。

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User Contributed Notes 3 notes

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laszlo dot heredy shift-two gmail etc ¶

8 years ago


Using is_string() on an object will always return false (even with __toString()).

<?php
class B {
  public function __toString() {
    return "Instances of B() can be treated as a strings!\n";
  }
}  

$b = new B();
print($b); //Instances of B() can be treated as a strings!
print(is_string($b) ? 'true' : 'false'); //false
?>

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Peter Barney ¶

4 years ago


As noted earlier, is_string() returns false on an object that has a __toString() method. Here is a simple way to do a check that will work:

<?php
// determine if the passed argument can be treated like a string.
function is_stringy($text) {
    return (is_string($text) || (is_object($text) && method_exists($text, '__toString' ));
}

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-1

jcours at numifinancial dot com ¶

1 year ago


is_string() of an integer or float returns false, so it might be useful to include an is_numeric() when checking if a value is stringy:

<?php
function is_stringy($val) {
  return (is_string($val) || is_numeric($val)
    || (is_object($val) && method_exists($val, '__toString')));
}
?>

Test code (which should print "vector N OK" for each test vector):
<?php
foreach ([[NULL, false], [false, false], [true, false],
  [0, true], [[], false], [0.1, true], ["x", true],
  ["", true], [new Exception("x"), true]] as $idx => $vector) {
  list ($val, $expected) = $vector;
  if (is_stringy($val) != $expected) {
    print ("mismatch at $idx\n");
    var_dump($val);
  } else {
    print ("vector $idx OK\n");
  }
}
?>

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