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[2004-12-28 18:36 UTC] phpbug at tore dot cc
Description:
------------
I have discoverd that a large amount of the php-scripts are using 'strlen' to count length of arbitrary strings.
strlen can not cope with arbitrary strings!
Code like will only show garbage values:
$a = fread($binaryfile,$count);
print strlen($a) . " number of bytes is read from
the binary file";
Reproduce code:
---------------
<?php
$s='';
print "<html>\n";
for($i=142;$i<256;$i++){
$s.=pack("C",$i);
$result = count_chars($s, 0);
$l=0;
for ($j=0; $j < 256; $j++) {
$l+=$result[$j];
}
print "<br>The variable s has the length: " .
strlen($s) . " (actual length) " . $l . "</br>\n";
}
print "</html>\n";
?>
Expected result:
----------------
The variable s has the length: 1 (actual length) 1
The variable s has the length: 1 (actual length) 2
The variable s has the length: 2 (actual length) 3
The variable s has the length: 3 (actual length) 4
The variable s has the length: 4 (actual length) 5
The variable s has the length: 5 (actual length) 6
The variable s has the length: 6 (actual length) 7
The variable s has the length: 7 (actual length) 8
The variable s has the length: 8 (actual length) 9
The variable s has the length: 9 (actual length) 10
The variable s has the length: 10 (actual length) 11
The variable s has the length: 11 (actual length) 12
.
.
.
The variable s has the length: 64 (actual length) 111
The variable s has the length: 65 (actual length) 112
The variable s has the length: 65 (actual length) 113
The variable s has the length: 66 (actual length) 114
Actual result:
--------------
The variable s has the length: 1 (actual length) 1
The variable s has the length: 2 (actual length) 2
The variable s has the length: 3 (actual length) 3
The variable s has the length: 4 (actual length) 4
The variable s has the length: 5 (actual length) 5
The variable s has the length: 6 (actual length) 6
The variable s has the length: 7 (actual length) 7
The variable s has the length: 8 (actual length) 8
The variable s has the length: 9 (actual length) 9
The variable s has the length: 10 (actual length) 10
The variable s has the length: 11 (actual length) 11
The variable s has the length: 12 (actual length) 12
.
.
.
The variable s has the length: 111 (actual length) 111
The variable s has the length: 112 (actual length) 112
The variable s has the length: 113 (actual length) 113
The variable s has the length: 114 (actual length) 114
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Last updated: Fri Oct 31 20:00:01 2025 UTC |
How about: <?php $s=pack("C",143); $result = count_chars($s, 0); print "The variable s has the length: " . strlen($s) . " (actual length) " . $result[143] . "\n"; ?> Gives printout: The variable s has the length: 0 (actual length) 1 The 'pack' creates a bit-string with a length of 1 char. The 'strlen' should should recognize it as a char with length 1. As you can see below 'strlen' does not only miscalculates the string length for the char 143.Sorry, my mistake! It seems to work on one char long strings. I made a better script (still avoiding loops...). <?php $s=pack("C*",0x8e,0x8f); $t=pack("C*",0x8e); $u=pack("C*",0x8e,0x8f,0x90); print "The variable s has the length: " . strlen($s) . "\n"; print "The variable t has the length: " . strlen($t) . "\n"; print "The variable u has the length: " . strlen($u) . "\n"; ?> Result: The variable s has the length: 1 The variable t has the length: 1 The variable u has the length: 2 The result should be: The variable s has the length: 2 The variable t has the length: 1 The variable u has the length: 3 Since s=2 chars, t=1 char and u 3 chars long. Lets try another test with 7 bit chars. <?php $s=pack("C*",0x30,0x31); $t=pack("C*",0x30); $u=pack("C*",0x30,0x31,0x32); print "The variable s has the length: " . strlen($s) . "\n"; print "The variable t has the length: " . strlen($t) . "\n"; print "The variable u has the length: " . strlen($u) . "\n"; ?> Result: The variable s has the length: 2 The variable t has the length: 1 The variable u has the length: 3 As expected. No problem with low values on the chars.