Checking string for whitespace

Question

Is there a way I can check for whitespace?

For example, I DO NOT want to check for whitespace such as this...

$string = "The dog ran away!"; and have it output Thedogranaway!

I want to check if there if the entry is ALL whitespace and whitespace only? ...and have it output the error!

Basically, I don't want to be able to enter all whitespace, and still have it do the mysql_query.
Also, is there a way I can strip all the whitespace before the string, and not from the rest of the string?

$string = " "WHITESPACE HERE" The dog ran away!";

if(empty($string) OR $string == " "){ // crappy example of what i'm trying to do
echo "Try again, please enter a message!"; // error
} else {
mysql_query("UPDATE users SET mesg='$string'")or die(mysql_error()); // do something
echo $post;
}

score 7 · Answer 1 · answered Nov 14 '09 at 03:49

7

How about:

if (strlen(trim($string)) == 0)

or, the possibly more efficient:

if (trim($string) == '')

or, you could use a regular expression:

if (preg_match("/^\s+$/", $string) != 0)

answered Nov 14 '09 at 03:49

James McNellis

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or `trim($string) == ''` might be slightly more efficient? – mpen Nov 14 '09 at 03:50
It might be; it depends on whether PHP stores the length of the string or if it null-terminates strings (I don't know which it uses). If it stores the length, both will perform about equally; if it uses null-terminated strings, performing a string comparison would probably be faster. – James McNellis Nov 14 '09 at 03:55
Well, if `strlen` performs equal or worse, it's better to go with the safer bet. Not that it really matters unless you're doing this 8 billion times. – mpen Nov 14 '09 at 04:32
I agree. I have to say, though, in terms of both elegance and raw performance, GZipp's answer is arguably the best of all the options presented on this page, by far. – James McNellis Nov 14 '09 at 05:56

score 7 · Accepted Answer · answered Nov 14 '09 at 03:59

7

There is also ctype_space (the easiest, imo, and made to do just this, without doing a bunch of unnecessary string manipulation):

$str = "   \r\n   \t  ";
if (ctype_space($str)) {
    echo 'All whitespace';
}
// All whitespace

answered Nov 14 '09 at 03:59

GZipp

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+1 for introducing me to a PHP function I've never used before. – James McNellis Nov 14 '09 at 04:03
I'm glad. :) It seems to me that all the ctype functions are relatively unknown and underused, even though they've been there since early PHP 4. – GZipp Nov 14 '09 at 04:09
Ended up using this, so much easier. – homework Nov 14 '09 at 09:42

score 2 · Answer 3 · answered Nov 14 '09 at 03:51

2

if ( trim($string) ) {
    // string contains text
}
else {
    // string contains only spaces or is empty
}

answered Nov 14 '09 at 03:51

Galen

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trim($string) evaluates to true if it is not an empty string? – jaywon Nov 14 '09 at 03:55
1

In PHP, an empty string _and_ the string `"0"` both evaluate to `false`. This fails for the latter case. – James McNellis Nov 14 '09 at 04:01

jaywon · Answer 4 · 2009-11-14T03:57:43.017

1

You can use the trim() function on an empty string:

if (strlen(trim($string)) == 0){
   //do something
}else{
  // do something else
}

To trim leading white space:

ltrim($string)

In the previous example " This is text" would return "This is text". Also trim() would achieve the same result, but trim() removes whitespace before and after the string.

edited Nov 14 '09 at 03:57

answered Nov 14 '09 at 03:51

jaywon

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score 1 · Answer 5 · answered Nov 14 '09 at 03:52

1

Maybe you are looking for a trim() method. In Java it would be String.trim(). I don't know how it should looks like in php, however this link might help http://php.net/manual/en/function.trim.php

answered Nov 14 '09 at 03:52

nandokakimoto

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Checking string for whitespace

5 Answers5