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strlen() and UTF-8 encoding
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I have a string with this content :
$myString = 'Câmara de Dirigentes Lojistas';
This string have 29 chars. BUT when i call strlen, it returns 30 ! Even when i call var_dump($myString), that's the result :
114:string 'Câmara de Dirigentes Lojistas' (length=30)
What is going on here ? Maybe the problem is related to the special char â ?
That's the right behavior since you are using UTF-8 encoding.
Please see this note on strlen() documentation
Note:
strlen() returns the number of bytes rather than the number of characters in a string.
As your string have multi-byte characters (â), PHP uses two bytes to represent it.
To have the right string length, you must use the mb_strlen() function:
mb_strlen("â"); // 1
strlen("â"); // 2
There are several definitions of the "length" of a string, because there are a variety of tricks used to represent the huge range of accented characters, variants, and non-alphabetic scripts used around the world.
The number of bytes the string takes up. This is the easiest to calculate, but not always what is expected. For instance, in UTF-16, every code point takes up either 2 or 4 bytes; in UTF-8, code points take up 1, 2, 3, or 4 bytes. This is what strlen and most PHP functions work with.
The number of "code points": separate symbols in the character set. This is the next easiest, and the next most common, but is generally a compromise between bytes and "graphemes" (see below) - there aren't many cases where it's particularly useful to count é as 2 "characters" just because it's represented with a combining diacritic. In PHP you can use mb_strlen to count these, telling it your string's character encoding.
The number of "graphemes": separate symbols a reader would recognise. This is the most intuitive meaning, but the hardest for a computer to define. In PHP you can use grapheme_strlen, as long as you have ensured your string is encoded as UTF-8.
There is an issue with the character â as it is a special character which uses a different encoding. Characters like this are actually double characters this is why its giving 30 and not 29
To fix this, you need to use mb_strlen() with encoding
$myString = 'Câmara de Dirigentes Lojistas';
echo mb_strlen($myString,'utf8')
NOTE : If mb_strlen is undefined, then you will have to enable mb extension in your php settings
Interestingly the â char exists in extended ascii, i.e. it can be represented by just one byte, you can try it with this code:
$str = utf8_decode('Câmara de Dirigentes Lojistas');
echo 'length is ' . strlen($str);
that will output length is 29.
So as you see the thing is that when a char is not plain ascii (127 char ascii table) then PHP assumes UTF-8 automatically.
I have a large string $string that when applied to md5(), give me
c4ca4238a0b923820dcc509a6f75849b
The length is 32, I want to reduce it, so
base64_encode(md5($string, true));
xMpCOKC5I4INzFCab3WEmw==
Removing the last two == it give me a string with length = 22.
Are there any other better algorithms?
I am not sure you realised that md5 is a hash function, and therefore irreversible. If you do not care about reversibility, you could just as well trim the md5 hash (or any hash of your liking*) down to an arbitrary number of characters. All this would do is increase the likelihood of collision (I feel this does not produce an uniform distribution though).
If you are looking for a reversible (ie. non-destructive) compression, then do not reinvent the wheel. Use the built-in functions, such as gzdeflate() or gzcompress(), or other similar functions.
*Here is a list of hash functions (wikipedia) along with the size of their output.
I suppose the smallest possible "hash function" would be a parity bit :)
One better way would be to, instead of converting to binary to hexadecimal (as md5 does) and then converting the string to base64, instead convert from the hexadecimal md5 directly to base64.
Since hexadecimal is 16 bits per character, and base64 is 64 bits per character, every 2 hexadecimal characters will make up one base64 character.
To perform the conversion, you can do the following:
Split the string into sixteen 2 character chunks
The first character should be multiplied by 2 and added to the second (keeping in mind that A-F = 10-15).
This number can be matched to the base64 scheme using the table from here: https://en.wikipedia.org/wiki/Base64
This will result in a 16 character base64 string with the same value as the hexadecimal representation of the md5 string.
Theoretically, you could do the same for any base. If we had a way to encode base128 strings in ASCII, we could end up with an 8 character string. However, as the character set is limited, I think base64 is the highest base that is commonly used.
The smaller the length of the string you want .. the smaller the number of possible combination
Total Number of Possibility with reputation
Total Possibility = nr
Since we are dealing with base64 has the printable output this means we only have 64 characters
n = 64
If you are looking at 22 letters in length
nr = 6422 = 5,444,517,870,735,015,415,413,993,718,908,291,383,296 possibilities
Back to your question : Are there any better algorithm?
Truncate the string with a good hash to desired length you want since the total possibility and collision is fixed
$string = "the fox jumps over the lazy brown dog";
echo truncateHash($string, 8);
Output
9TWbFjOl
Function Used
function truncateHash($str, $length) {
$hash = hash("sha256", $str, true);
return substr(base64_encode($hash), 0, $length);
}
This encoding generates shorter string,
print base64_encode(hash("crc32b",$string,1));
output
qfQIdw==
Not sure if MD5 is the right choice for you, but i will assume that you have reason to stick with this algorithm and are looking for a shorter representation. There are several possibilities to generate a shorter string with different alphabets:
Option 1: Binary string
The shortest possbile form of an MD5 is it's binary representation, to get such a string you can simply call:
$binaryMd5 = md5($input, true);
This string you can store like any other string in a database, it needs only 16 characters. Just make sure you do a proper escaping, either with mysqli_real_escape_string() or with parametrized queries (PDO).
Option 2: Base64 encoding
Base64 encoding will produce a string with this alphabet: [0-9 A-Z a-z + /] and uses '=' as padding. This encoding is very fast, but includes the sometimes unwanted characters '+/='.
$base64Md5 = base64_encode(md5($input, true));
The output length will be always 24 characters for the MD5 hash.
Option 3: Base62 encoding
The base62 encoding only uses the alphabet [0-9 A-Z a-z]. Such strings can be safely used for any purpose like tokens in an URL, and they are very compact. I wrote a base62 encoder, which is able to convert binary strings to the base62 alphabet. It may not be the fastest possible implementation, but it was my goal to write understandable code. The same class could be easily adapted to different alphabets.
$base62Md5 = StoBase62Encoder::base62encode(md5($input, true));
The output length will vary from 16 to 22 characters for the MD5 hash.
Base 91 looks like the most space efficient binary to ASCII printable encoding algorithm (which is what it seems you want).
I've not seen the PHP implementation, but if your software has to work with others I'd stick to Base 64; it's well-known, lightning fast, and available everywhere.
Firstly, to answer your question: Yes, there is a better algorithm (if with "better" you mean "shorter").
Use the hash() function (which has been part of the PHP core and enabled by default since PHP 5.1.2.) with any of the adler32, fnv132, crc32, crc32b, fnv132 or joaat algorithms.
Without a more in-depth knowledge of your current situation, you might as well just pick whichever one you think sounds the coolest.
Here is an example:
hash('crc32b', $string)
I set up an online example you can play around with.
Secondly, I would like to point out that what you are asking is an almost exact duplicate of another question here on stackoverflow.
I read from your post that you are searching for a hashing algorithm and not compression.
There are various standard hashing algorithms in php out there. Have a look at PHP hashing functions.
Depending on what you want to hash there are different approches. Be careful and calculate the average collision probability.
However it seems you are searching for a 'compression' which outputs the minimum possible size of chars for a given string. If you do, then have a look at Lempel–Ziv–Welch (php implementation) or others.
Is there a native or inexpensive way to check for the length of a string in bytes in PHP?
See http://bytes.com/topic/php/answers/653733-binary-string-length
Relevant part:
"In PHP, like in C, the string ends with a zero-character, '\0', (char)
0, null-terminator, null-byte or whatever you like to call it."
No, that's not the case - PHP strings are stored with both the length and the
data, unlike C strings that just has one pointer and uses a terminator. They're
"binary-safe" - NUL doesn't terminate the string.
See the definition of zvalue_value in zend.h; the string part has both a "char
*val" and "int len".
Problems would start if you're using the mbstring.func_overload, which changes
how strlen() and the other functions work, and does try and treat strings as
strings of characters in a specific encoding rather than a string of bytes.
This is not the normal PHP behaviour.
The answer is that strlen should return the number of bytes regardless of the content of the string. For multi-byte character strings, you get the wrong number of characters, but the right number of bytes. However, you need to be certain you're not using the mbstring overload, which changes how strlen behaves.
In the event that you have mbstring overload set or your are developing for the platforms where you are unsure about this setting you can do the following:
$len=strlen(bin2hex($data))/2;
The reason why this works is that in Hex you are guaranteed to get 2 characters for all bytes that come from bin2hex (it returns two chars even for the initial binary 0).
Note that it will use significantly more resources than a normal strlen (afterall, so you should definitely not do that to the large amount of data if it's not absolutely necessary.
On php.org, someone was nice enough to create this function. Just multiply by 8 and you've got however many bits were in that string, as the function returns bytes.
The length of a string (textual data) is determined by the position of the NULL character which marks the end.
In case of binary data, NULL can be and often is in the middle of data.
You don't check the length of binary data. You have to know it beforehand. In your case, the length is 16 (bytes, not bits, if it is UUID).
As far as UUID validity is concerned, any 16-byte value is a valid UUID, so you are out of luck there.
Is there any PHP function that encodes a string to a int value, which later I can decode it back to a string without any key?
Sure, you can convert strings to numbers and vice versa. Consider:
$a = "" + 1
gettype($a) // integer
$b = "$a"
gettype($b) // string
You can also do type casting with settype().
If I misunderstood you and you want to encode arbitrary strings, consider using base64_encode() and bas64_decode(). If you want to convert the base 64 string representation to a base 10 integer, simply use base_convert().
And int has 4 or 8 bytes depending on the platform, and each character in a string is one byte (or more depending on encoding). So, you can only encode very small strings to integers, which basically makes the answer to your question: no.
What do you want to accomplish?
I would suspect not, since there are far more possible string combinations than integers within the MAX_INT.
Does it have to be an integer?
i'm convinced that what you think you want to do is not really what you want to do. :-) this just sounds like a silly idea. As another user has asked before:) what do you need this for? What are your intentions?
Well now that you mentioned that numbers and a-z letter are acceptable, then I have one suggestion, you could loop through the individual letters' ordinal value and display that as a two-digit hexadecimal. You can then convert these hexadecimals back to the ordinal values of the individual characters. Don't know what kind of characters are you about to encode, possibly you will need to use 4-characters per letter (e.g. String Peter would become 00700065007400650072 ) Well... have fun with that, I still don't really see the rationale for doing what you're doing.
op through the individual letters' ordinal value and display that as a two-digit hexadecimal. You can then convert these hexadecimals back to the ordinal values of the individual characters. Don't know what kind of characters are you about to encode, possibly you will need to use 4-characters per letter (e.g. String Peter would become 00700065007400650072 ) Well... have fun with that, I still don't really see the
There is no function for PHP but I recently wrote a class to encrypt and decrypt a string in PHP. You can look at it at: https://github.com/Lars-/PHP-Security-class
I am trying to send something to serial port (r232) with PHP.
I am using this class: http://www.phpclasses.org/browse/package/3679.html
The problem is that I am allowed to send only 1 byte.
But if I send something like "1", I am actually sending 49 (ASCII for 1).
Instead of send("1"), I tried with send(1) but it is no good, because this is integer which has 2 bytes.
So is there a way to send a "real" char, not ASCII equivalent?
The chr() function returns a character given by the integer for the corresponding ascii character.
It looks like the library is expecting characters as input. If you need to send the character which would encode to 0x01, you just send "\001". The function chr() would convert characters to integer values and would be no use here.
One more thing: The byte size of integers depends on the underlying system and is mostly 4 bytes.
I'm not sure what you are trying to accomplish. Are you trying to to send the integer 1? Not being familiar with the class, have you tried to give just the value 1 as an argument? If that doesn't work, try to wrap it with the chr() function.