(PHP 4, PHP 5)
is_string — 检测变量是否是字符串
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()。
jeroen at asystance dot nl (2012-10-17 21:22:16)
Note that this (and probably other is_* functions) behave differently with respect to lazy evaluation:
php > $v = '';
php > echo $v[0];
PHP Notice: Uninitialized string offset: 0 in php shell code on line 1
# As expected!
php > empty($v) && $v[0];
# As expected, this does not throw a notice, since $v[0] is never evaluated.
# However:
php > is_string($v) && $v[0];
PHP Notice: Uninitialized string offset: 0 in php shell code on line 1
slicky at newshelix dot com (2001-03-20 05:06:54)
Be aware that this function could result into unwanted results if you check single chars in an array.
For instance:
You have a simple string and want to repeat this string evertime it ends.
<?php
for ($i=0; $i < strlen($string);$i++){
if(!is_string($key[$x]))
$x = 0;
echo $key[$x];
$x++;
}
?>
This will print you out the key, but won't iterate it since $x won't be reset. is_string function will give out true at element in that string, even if it doesn't exist. for instance is_string $key[1000] while your string is just 10chars long.
However this doesn't matter just use $key[$x] == '' instead.
Of course you won't use this to iterate a string, but you might come across something where this get useful, for instance for a en/decrypt engine.