strcmp

lehal2 at hotmail dot com (2013-01-01 23:32:28)

i hope this will give you a clear idea how strcmp works internally.

<?php
$str1 = "b";
echo ord($str1); //98
echo "<br/>";
$str2 = "t";
echo ord($str2); //116
echo "<br/>";
echo ord($str1)-ord($str2);//-18
$str1 = "bear";
$str2 = "tear";
$str3 = "";
echo "<pre>";
echo strcmp($str1, $str2); // -18
echo "<br/>";
echo strcmp($str2, $str1); //18
echo "<br/>";
echo strcmp($str2, $str2); //0
echo "<br/>";
echo strcmp($str2, $str3); //4
echo "<br/>";
echo strcmp($str3, $str2); //-4
echo "<br/>";
echo strcmp($str3, $str3); // 0
echo "</pre>";
?>

jendoj at gmail dot com (2012-05-07 11:00:38)

If you rely on strcmp for safe string comparisons, both parameters must be strings, the result is otherwise extremely unpredictable.
For instance you may get an unexpected 0, or return values of NULL, -2, 2, 3 and -3.
strcmp("5", 5) => 0
strcmp("15", 0xf) => 0
strcmp(61529519452809720693702583126814, 61529519452809720000000000000000) => 0
strcmp(NULL, false) => 0
strcmp(NULL, "") => 0
strcmp(NULL, 0) => -1
strcmp(false, -1) => -2
strcmp("15", NULL) => 2
strcmp(NULL, "foo") => -3
strcmp("foo", NULL) => 3
strcmp("foo", false) => 3
strcmp("foo", 0) => 1
strcmp("foo", 5) => 1
strcmp("foo", array()) => NULL + PHP Warning
strcmp("foo", new stdClass) => NULL + PHP Warning
strcmp(function(){}, "") => NULL + PHP Warning

hrodicus at gmail dot com (2011-02-28 06:40:17)

Note a difference between 5.2 and 5.3 versions
echo (int)strcmp('pending',array());
will output -1 in PHP 5.2.16 (probably in all versions prior 5.3)
but will output 0 in PHP 5.3.3
Of course, you never need to use array as a parameter in string comparisions.

hm2k at php dot net (2010-08-02 04:41:38)

Don't forget the similar_text() function...
http://php.net/manual/en/function.similar-text.php

Rob Wiesler (2009-07-21 12:48:21)

One big caveat - strings retrieved from the backtick operation may be zero terminated (C-style), and therefore will not be equal to the non-zero terminated strings (roughly Pascal-style) normal in PHP. The workaround is to surround every `` pair or shell_exec() function with the trim() function. This is likely to be an issue with other functions that invoke shells; I haven't bothered to check.

On Debian Lenny (and RHEL 5, with minor differences), I get this:

====PHP====
<?php
$sz = `pwd`;
$ps = "/var/www";

echo "Zero-terminated string:<br />sz = ".$sz."<br />str_split(sz) = "; print_r(str_split($sz));
echo "<br /><br />";

echo "Pascal-style string:<br />ps = ".$ps."<br />str_split(ps) = "; print_r(str_split($ps));
echo "<br /><br />";

echo "Normal results of comparison:<br />";
echo "sz == ps = ".($sz == $ps ? "true" : "false")."<br />";
echo "strcmp(sz,ps) = ".strcmp($sz,$ps);
echo "<br /><br />";

echo "Comparison with trim()'d zero-terminated string:<br />";
echo "trim(sz) = ".trim($sz)."<br />";
echo "str_split(trim(sz)) = "; print_r(str_split(trim($sz))); echo "<br />";
echo "trim(sz) == ps = ".(trim($sz) == $ps ? "true" : "false")."<br />";
echo "strcmp(trim(sz),ps) = ".strcmp(trim($sz),$ps);
?>

====Output====
Zero-terminated string:
sz = /var/www 
str_split(sz) = Array ( [0] => / [1] => v [2] => a [3] => r [4] => / [5] => w [6] => w [7] => w [8] => ) 

Pascal-style string:
ps = /var/www
str_split(ps) = Array ( [0] => / [1] => v [2] => a [3] => r [4] => / [5] => w [6] => w [7] => w ) 

Normal results of comparison:
sz == ps = false
strcmp(sz,ps) = 1

Comparison with trim()'d zero-terminated string:
trim(sz) = /var/www
str_split(trim(sz)) = Array ( [0] => / [1] => v [2] => a [3] => r [4] => / [5] => w [6] => w [7] => w ) 
trim(sz) == ps = true
strcmp(trim(sz),ps) = 0

wsogmm at seznam dot cz (2009-05-16 08:45:03)

Just a short comment to the note of arnar at hm dot is: md5() is a hash function and therefore it may happen (although it is very unlikely) that the md5() checksums of two different strings will be equal (hash collision) ...

arnar at hm dot is (2009-05-15 07:51:06)

Sometimes when you compare two strings that look "the same", you will find that they aren't. If you don't want to bother finding out why, then this is a simple solution:
$string = implode(str_split($string));
Converting the strings to md5 is also a nice method to see if they're equal.
md5($str1)."\n";
md5($str2)."\n\n";
____________
Arnar Yngvason
ThinkSoftware

nullhility at gmail dot com (2009-03-15 02:36:41)

For those that are confused about the way this function works:

<?php
$str1 = 'a';
$str2 = 'b';
var_dump(strcmp($str1, $str2)); //int(-1)
?>

Alphabetically 'a' precedes 'b'. If we view the strings as values 'a' is less than 'b' and therefore the function returns -1.

If we were searching through an alphabetically sorted list we'd have a numerical index ($i) and compare the search string ($sstr) against each member of the string list ($slist), using strcmp we can check whether to go "up"($i++) or "down"($i--) through this list. 

Here's the example function:
<?php
function strInList ($sstr)
{
    $slist = array('a', 'b', 'c', 'd', 'e' /* etc */);
    
    $i = sizeof($slist) / 2; //start the index in the middle
    
    while ($i < sizeof($slist) && $i >= 0) { //constrain $i to the scope of $slist
        
        $cmp = strcmp($slist[$i], $sstr); 
        
        if ($cmp > 0) { //alphabetically, $slist[$i] procedes $sstr
            $i--; //move DOWN the list
        } else if ($cmp < 0) { //alphabetically, $slist[$i] precedes $sstr
            $i++; //move UP the list
        } else if ($cmp == 0) { //$slist[$i] occurs neither before nor after $sstr
            return true; //successful match
        }
    }
    return false; //The index fell out of the list scope, with no match made
}
?>

g-lock at nv-net.ru (2008-06-18 23:08:00)

Here is my function to compare russian words.
You can replace $abc to your alphabet.
function strcmp_rus($str1, $str2)
{
$abc = "АБВГДЕЁЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯ
абвгдеёжзийклмнопрстуфхцчшщъыьэюя";
$len = min(strlen($str1), strlen($str2));
for ($i = 0; $i < $len; $i++)
{
$s1 = strlen($abc);
$s2 = strlen($abc);
for ($j = 0; $j < strlen($abc); $j++) if ($str1[$i] == $abc[$j]) $s1 = $j;
for ($k = 0; $k < strlen($abc); $k++) if ($str2[$i] == $abc[$k]) $s2 = $k;
if ($s1 < $s2) return -1;
else if ($s1 > $s2) return 1;
}
return 0;
}

nobody@nogroup (2007-08-23 07:59:30)

To Monsieur Egmont and 'php or die', use setlocale and strcoll to compare strings in languages such as German, Swedish that use accented characters, and strings of non-latin script.

M. Egmond (2006-08-22 03:21:24)

php dot or dot die at phpuser dot net wrote that he had an unexpected difference in comparing between case sensitive and insensitive. They key there is that the case insensitive comparison converts both strings to lowercase before comparing. Since the underscore character is in a different place when compared to an uppercase or lowercase string, the result is different.
There is no 'clear' order of punctuation and other characters in or around the alphabet. Most code assumes ASCII order in which case there are several characters before both upper- and lowercase, a few inbetween, and some after both upper- and lowercase.
Note also many other/older implementations of sorting sort accented character wrong since they appear after all other alphabetical characters in most charactersets. There is probably a function in PHP to take this into account though.
Therefore I would not recommend to make a detailed assumption on how punctuation and other characters sort in relation to alphabetical characters. If sorting these characters at a specific place and in a specific order is important for you, you should probably write a custom string comparison function that does it the way you want. Usually it's sufficient to have a consistent sorting order though, which is what you get by using either strcmp, or strcasecmp consistently.

jeff at skrysak dot com (2006-08-03 07:36:53)

The definition of return values of this function is listed correctly on this page, however, there is a common misconception in the notes posted here previously from users.
A previous poster said:
If $str1 == $str2 strcmp return 0.
If $str1? > $str2 strcmp return 1.
If $str1? < $str2 strcmp return -1.
That is incorrect, please look at the definition of the function
at the top of this page. It returns less than 0 if str1 is less than str2. Note the phrase "less than", it does not return just -1, but any negative value. The same happens when str1 is greater than str2, but it returns a positive, non-zero value. It returns a positive value that can be 1, or any number thereafter.
strcmp() returns a number that is the difference between the two strings starting with the last character that was found to be similar.
Here is an example:
$output = strcmp("red", "blue");
The variable $output with contain a value of 16

robertb at littleNOSPAMcutie dot net (2006-04-05 07:19:20)

S dot Radovanovic suggested:

"So my conclusion is that when comparing string, you'd better not make use of == (use strmp or === instead). For integer comparisons the == equation can be usefull, since our values will always be casted to an integer (1 == "1" returns true)."

When I tried this, I ran into a problem with parameters passed in the URL.  I forgot that a parameter that is not supplied wouldn't be a string, so this code -- which I expected to default to the current year -- didn't work:

<?php
// Did we get a parameter?
if ($year === '') {
    // Default to current year
    $temp = getdate(); 
    $year = $temp['year'];    
}

$fname = "magic{$year}.txt";

if (file_exists($fname) == FALSE) {
  echo "<h2>Data file doesn't exist</h2>";
  exit;
}
?>

Since $year was uninitialized, it didn't exactly equal '', and the file wasn't found.  I went back to == in this case.

However, I did heed your advice when looking for a particular value ($debug === 'Y'), instead of looking for the lack of a value.  Thanks!

php dot or dot die at phpuser dot net (2006-02-15 02:19:56)

I've a strange problem. I tried to compare string in the same order oracle does.
The strange thing is:
strcmp('ACQUE_SOTTERRANEE','ACQUE_SOTT_ORAC')
//result is -1
strcasecmp('ACQUE_SOTTERRANEE','ACQUE_SOTT_ORAC')
//result is 6
I'm surprised for the opposite result!
The correct order (oracle ascending order) is:
1- ACQUE_SOTTERRANEE
2- ACQUE_SOTT_ORAC

francis at flourish dot org (2005-12-08 06:57:36)

If you want to strings according to locale, use strcoll instead.

element @ no spam dot net (2005-02-19 15:42:37)

When using strcmp to compare results received from a form, keep in mind that the way you decide to encapsulate the value of the form will have an effect on your strcmp() results.
Example:
<input type="post" name="user[0]" value="abc">
<input type="post" name="user[1]" value='abc'>
strcmp() will not return the values sent from this form as "0".
However, by using single-quotes or double-quotes to encapsulate BOTH values, strcmp() will return a "0" result.

S dot Radovanovic at TriMM dot nl (2005-02-07 06:36:20)

One thing to note in comparison with ==

When we make a comparison with == php automaticly converts strings to integers when either side of the comparison is an integer, f.e.:
<?
$value = 0;
if($value == "submit") {
    echo "Let's submit";
}
?>
Above would be succesful, since "submit" is converted to an integer (eq 0) and the equation is would return true; (that's why (1 == "1submit") would also return true)

That's why we should use strcmp or === (checks type also), for string comparisons.

So my conclusion is that when comparing string, you'd better not make use of == (use strmp or === instead). For integer comparisons the == equation can be usefull, since our values will always be casted to an integer (1 == "1" returns true).

x123 at bestof-inter dot net (2004-10-29 18:43:51)

Please tell what you mean by "alphabetically" and when you say 
"because of the way it works, it is not very useful..." or
"I get strange results, 1 for strings that are equal, etc." :
give an example where it does not work and/or show where your script works better!
(To test some PHP code, it is sufficient to have a file of 3 lines:
<form action='' method=POST><input type=submit value=Evaluate>
<textarea id=c><?=$c=stripslashes($_POST['c'])?></textarea>
<br>Result of the above:<pre><?=eval($c)?></pre></form>)

Imagine how much time is lost for visitors trying to figure out what your program does differently from strcmp ?

Imagine how much resources are wasted if PHP users are made to think that PHP functions don't work well and use the EXTREMELY inefficient routines proposed below (e.g. a string comparision routine that uses substr(...,$i,1) to access individual caracters...!)

If the documentation says 'binary safe' this should mean that strings are compared byte by byte (according to internal format)
- if strcmp() does instead use locale collation tables, this should be clearly mentioned in the documentation.

pabloATnkstudiosDOTnet (2004-06-01 11:36:53)

Just note that the documentation about the function returns is a little confused.
So...
If $str1 == $str2 strcmp return 0.
If $str1 > $str2 strcmp return 1.
If $str1 < $str2 strcmp return -1.
Pablo Rosciani
http://pablo.rosciani.com.ar

jcanals at totsoft dot com (2004-01-30 18:05:23)

Some notes about the spanish locale. I've read some notes that says "CH", "RR" or "LL" must be considered as a single letter in Spanish. That's not really tru. "CH", "RR" and "LL" where considered a single letter in the past (lot of years ago), for that you must use the "Tradictional Sort". Nowadays, the Academy uses the Modern Sort and recomends not to consider anymore "CH", "RR" and "LL" as a single letter. They must be considered two separated letters and sort and compare on that way.
Ju just have to take a look to the Offial Spanish Language Dictionary and you can see there that from many years ago there is not the separated section for "CH", "LL" or "RR" ... i.e. words starting with CH must be after the ones starting by CG, and before the ones starting by CI.

gregd at sad dot net (2003-09-08 11:49:17)

In cases when you need to compare a line from a just parsed file stream to match a user-defined "nametag" (useful for parsing ini and configuration files), keep in mind the 'end of line' tags as well:
// nametag to look for in a file (notice a required "\r\n" at the end)
$nametag = "[System]\r\n";
// ...assuming the file has been aready opened for reading and the stream is bound to $filehandle... parse the file until an EOF or $nametag encountered.
while (!feof ($handle))
{
$buffer = fgets($filehandle);
if (strcmp($nametag, $buffer) == 0)
{
// at this point "[System]" is found, do additional parsings...
break;
}
}

admin[nospam] at pretend dot tk (2003-06-17 19:44:15)

Reguarding the above note on language specific string comparisons, LL and RR are also single letters in the Spanish language.

mnunemacher at datility dot net (2003-04-27 15:40:15)

Because of the way this function works, it's not very useful for ordering strings alphabetically. If you're trying to alphabetize a list of strings (like a dictionary does), you may want to use the following functions instead:
-----------------
// Returns 1 if $str1 comes before $str2 alphabetically
// Returns -1 if $str1 comes after $str2 alphabetically
// Returns 0 if $str1 and $str2 are the same
function orderAlpha ( $str1, $str2 ) {
$limit = null;
if ( strlen( $str1 ) > strlen( $str2 ) ) {
$limit = strlen( $str2 );
} else {
$limit = strlen( $str1 );
}
for ( $i = 0;$i < $limit;$i++ ) {
if ( substr( $str1, $i, 1 ) > substr( $str2, $i, 1 ) ) {
return 1;
} else if ( substr( $str1, $i, 1 ) < substr( $str2, $i, 1 ) ) {
return -1;
}
}
if ( strlen( $str1 ) > strlen( $str2 ) ) {
return 1;
} else if ( strlen( $str1 ) < strlen( $str2 ) ) {
return -1;
}
return 0;
}
// Case insensitive version of orderAlpha
function orderiAlpha ( $str1, $str2 ) {
return orderAlpha( strtolower( $str1 ), strtolower( $str2 ) );
}
-----------------

ahmed at somantic dot net (2003-03-23 00:52:22)

For some reason the strcmp fails for this function if the $item_to_compare->ID = "AB123" or some similar string. This happened even though $ID = "AB123":
<pre>
function item_exists($ID)
{
// returns 0 for error
global $item_list; // this is an array of class objects
if (is_array($item_list))
{
foreach ($item_list as $key => $item_to_compare)
{
if (!strcmp($item_to_compare->ID, $ID))
{
unset ($item_list);
return $key;
}
}
}
// Else fail
unset ($item_list);
return 0;
}
</pre>
So I was forced to do this:
<pre>
function item_exists($ID)
{
// returns 0 for error
global $item_list;
if (is_array($item_list))
{
for($i = 0; $i < count($item_list); $i++)
{
if (!strcmp($item_list[$i]->ID, $ID))
{
unset ($item_list);
return $i;
}
}
}
// Else fail
unset ($item_list);
return 0;
}
</pre>

izhan dot khalib at acpibhd dot com (2002-12-16 23:13:19)

I have tried the strcmp function. Pls be very carefull. The string comparison must exactly "equal". So many people had confused.
I.e
My program read a string from test.txt file to get the
"[company name]" string.
// get contents of a file into a string
$filename = "test.txt";
$fd = fopen ($filename, "rb");
$contents = fread ($fd, filesize ($filename));
for($i=0;$i<strpos($contents, "]")+1;$i++)
{
//print $contents[$i];
//$a=trim($contents[$i]);
$a=$contents[$i];
echo $a;
//echo $i;
}
$str2="[companyname]";
// this comparison will resulted on greater (1), $result=1
//please remember $tempvariable[2] != $tempvariable (is not equal)
$result = strcmp(strtolower($a),strtolower($str2));
//this comparison working properly, $result=0
//$result = strcmp(strtolower($a),strtolower($str2[12]));
echo $result;
if ($a==$str2[12]) //double check the equality of string
{
echo "read the NextLine"; }
else {
echo "not equal";
}
//end
fclose ($fd);
?>
I hope the above example will help you.

madsen at sjovedyr dot dk (2002-10-02 11:59:33)

It's definitely worth noting that the return-values of strcmp() when used for i.e. password-checking is the oposite of that of the ==-operator.
I.e.:
$pw1 = "yeah";
$pw2 = "yeah";
if (strcmp($pw1, $pw2)) { // This returns false.
// $pw1 and $pw2 are NOT the same.
} else {
// $pw1 and $pw2 are the same.
}
Where the use of the == operator would give us.:
if ($pw1==$pw2) { // This returns true.
// $pw1 and $pw2 are the same.
} else {
// $pw1 and $pw2 are NOT the same.
}
Additionally, to check if $pw1 and $pw2 are of the same type you can use the === operator.

(2002-08-27 06:45:47)

anonymous at anon dot com (2001-06-14 16:51:23)

As mentioned above...be careful of trailing whitespace when making string comparisons...to be sure that you are rid of it all, use the trim() function.

owen at cips dot nokia dot com (2000-11-03 16:23:02)

Regarding bizarre return values from str*cmp(), I was having similar troubles until I realized that I was attempting to compare a string with HTML formatting with its plain-text equivilant. The formatted string was an <OPTION> value, so the HTML was rendered without the <b> and <i> formatting I was using. Consequently the formatted and unformatted strings were rendered identically in the browser. D'oh!

phpnotes at travelersweb dot com (2000-07-31 20:18:48)

Here is a quick note to explain what is meant by > and <. I wrote a script to compare results. If a string is closer to 'A' in the alphabet, it is < the other string. Here is the output hope this save saves people lots of time:
acc = acc | ac < acc
accc > acc | acd > acc
acb < acc | acb < accc
acb < accd | bcc > acc
bcc > acc | bcca > acc
bcc > acca | 1bcc < acca
bcc < bcc1 | bcc1 > bcc
1bcc < bcc | 1bcc < 1bcd
1bcd > 1bcc | _bcc < bcc
bcc > _bcc | ;bcc < bcc
bcc > ;bcc | bcc < bcc;
bcc; = bcc;

Jesse at bend dot com (2000-07-26 22:15:49)

Well, I am using PHP 4.0 and both strcmp and strcasecmp appear to be giving me very arbitrary and incomprehensible results. When I input strings, it appears that "equal" strings return "1", as well as some unequal strings, and that if the first argument is "smaller" then I *tend* to get negative numbers, but sometimes I get 1, and if larger I *tend* to get numbers larger than 1..
both strcmp and strcasecmp are thus rendered totally unuseable for me in order to either alphebetize or compare strings for inequality.

frewuill at merlin-corp dot com (2000-02-28 14:49:38)

Hey be sure the string you are comparing has not special characters like '\n' or something like that.