(PHP 4, PHP 5, PHP 7, PHP 8)
is_string — 查找变量的类型是否是字符串
value要计算的变量。
如果 value 是类型 string，返回
true，否则返回 false。
示例 #1 is_string() 示例
<?php
$values = array(false, true, null, 'abc', '23', 23, '23.5', 23.5, '', ' ', '0', 0);
foreach ($values as $value) {
echo "is_string(";
var_export($value);
echo ") = ";
echo var_dump(is_string($value));
}
?>以上示例会输出：
is_string(false) = bool(false)
is_string(true) = bool(false)
is_string(NULL) = bool(false)
is_string('abc') = bool(true)
is_string('23') = bool(true)
is_string(23) = bool(false)
is_string('23.5') = bool(true)
is_string(23.5) = bool(false)
is_string('') = bool(true)
is_string(' ') = bool(true)
is_string('0') = bool(true)
is_string(0) = bool(false)
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($b) ? 'true' : 'false'); //false
?>As noted earlier, is_string() returns false on an object that has a __toString() method. Here is a simple way to do a check that will work:
<?php
// determine if the passed argument can be treated like a string.
function is_stringy($text) {
return (is_string($text) || (is_object($text) && method_exists($text, '__toString' ));
}is_string() of an integer or float returns false, so it might be useful to include an is_numeric() when checking if a value is stringy:
<?php
function is_stringy($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");
}
}
?>