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.
strcmp
Description
int strcmp ( string str1, string str2 )Returns < 0 if str1 is less than str2; > 0 if str1 is greater than str2, and 0 if they are equal.
Note that this comparison is case sensitive.
See also ereg(), strcasecmp(), substr(), stristr(), strncasecmp(), strncmp(), and strstr().
add a note
User Contributed Notes
M. Egmond
22-Aug-2006 06:21
22-Aug-2006 06:21
jeff at skrysak dot com
03-Aug-2006 10:36
03-Aug-2006 10:36
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 $output with contain a value of 16
robertb at littleNOSPAMcutie dot net
05-Apr-2006 10:19
05-Apr-2006 10:19
S dot Radovanovic suggested:
"So my conclusion is that when comparing string, you'd better not make use of == (use strmp or === instead). For integer comparisons the == equation can be usefull, since our values will always be casted to an integer (1 == "1" returns true)."
When I tried this, I ran into a problem with parameters passed in the URL. I forgot that a parameter that is not supplied wouldn't be a string, so this code -- which I expected to default to the current year -- didn't work:
<?php
// Did we get a parameter?
if ($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
15-Feb-2006 06:19
15-Feb-2006 06:19
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
08-Dec-2005 10:57
08-Dec-2005 10:57
If you want to strings according to locale, use strcoll instead.
element @ no spam dot net
20-Feb-2005 07:42
20-Feb-2005 07:42
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
07-Feb-2005 10:36
07-Feb-2005 10:36
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
30-Oct-2004 09:43
30-Oct-2004 09:43
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
02-Jun-2004 02:36
02-Jun-2004 02:36
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
31-Jan-2004 10:05
31-Jan-2004 10:05
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
09-Sep-2003 02:49
09-Sep-2003 02:49
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
18-Jun-2003 10:44
18-Jun-2003 10:44
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
28-Apr-2003 06:40
28-Apr-2003 06:40
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
23-Mar-2003 04:52
23-Mar-2003 04:52
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
17-Dec-2002 03:13
17-Dec-2002 03:13
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
03-Oct-2002 02:59
03-Oct-2002 02:59
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.
27-Aug-2002 09:45
In summary, strcmp() does not necessarily use the ASCII code order of each character like in the 'C' locale, but instead parse each string to match language-specific character entities (such as 'ch' in Spanish, or 'dz' in Czech), whose collation order is then compared. When both character entities have the same collation order (such as 'ss' and '' in German), they are compared relative to their code by strcmp(), or considered equal by strcasecmp().
The LC_COLLATE locale setting is then considered: only if LC_COLLATE=C or LC_ALL=C does strcmp() compare strings by character code.
Generally, most locales define the following order:
control, space, punctuation and underscore, digit, alpha (lower then upper with Latin scripts; or final, middle, then isolated, initial with Arabic script), symbols, others...
With strcasecmp(), the alpha subclass is ignored and consider all forms of letters as equal.
Note also that some locales behave differently with accented characters: some consider they are the same letter as the unaccented letter (with a minor collation order, e.g. French, Italian, Spanish), some consider they are distinct letters with an independant collation order (e.g. in the C locale, or in Nordic languages).
Finally, the collation string is not considering individual characters but instead groups of characters that form a single letter:
- for example "ch" or "CH" in Spanish which is always after all other strings beginning with 'c' or 'C', including "cz", but before 'd' or 'D';
- 'ss' and '' in German;
- 'dz', 'DZ' and 'Dz' in some Central European languages written with the Latin script...
- UTF-8, UTF-16 (Unicode), S-JIS, Big5, ISO2022 character encoding of a locale (the suffix in the locale name) first decode the characters into the UCS4/ISO10646 code position before applying the rules of the language indicated by the main locale...
So be extremely careful to what you consider a "character", as it may just mean a encoding byte with no significance in the string collation algorithm: the first character of the string "cholera" in Spanish is "ch", not "c" !
anonymous at anon dot com
15-Jun-2001 07:51
15-Jun-2001 07:51
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.
timpie2000 at zeelandnet dot nl
28-Dec-2000 08:00
28-Dec-2000 08:00
[Ed Note:
See strcasecmp().
--irc-html@php.net]
You can make this function case insentive by using
strcmp(strtolower($a) , strtolower ($b));
owen at cips dot nokia dot com
04-Nov-2000 08:23
04-Nov-2000 08:23
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
01-Aug-2000 11:18
01-Aug-2000 11:18
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: <BR>
acc = acc | ac < acc <BR>
accc > acc | acd > acc <BR>
acb < acc | acb < accc <BR>
acb < accd | bcc > acc <BR>
bcc > acc | bcca > acc <BR>
bcc > acca | 1bcc < acca <BR>
bcc < bcc1 | bcc1 > bcc <BR>
1bcc < bcc | 1bcc < 1bcd <BR>
1bcd > 1bcc | _bcc < bcc <BR>
bcc > _bcc | ;bcc < bcc <BR>
bcc > ;bcc | bcc < bcc; <BR>
bcc; = bcc;
Jesse at bend dot com
27-Jul-2000 01:15
27-Jul-2000 01:15
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
29-Feb-2000 06:49
29-Feb-2000 06:49
Hey be sure the string you are comparing has not special characters like '\n' or something like that.