base64_decode
(PHP 4, PHP 5)
base64_decode — Decodes data encoded with MIME base64
Description
string base64_decode
( string
$data
[, bool $strict = false
] )
Decodes a base64 encoded data.
Parameters
-
data -
The encoded data.
-
strict -
Returns
FALSEif input contains character from outside the base64 alphabet.
Return Values
Returns the original data or FALSE on failure. The returned data may be
binary.
Changelog
| Version | Description |
|---|---|
| 5.2.0 | strict added |
Examples
Example #1 base64_decode() example
<?php
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw==';
echo base64_decode($str);
?>
The above example will output:
This is an encoded string
Коментарии
This function supports "base64url" as described in Section 5 of RFC 4648, "Base 64 Encoding with URL and Filename Safe Alphabet"
<?php
function base64url_decode($base64url)
{
$base64 = strtr($base64url, '-_', '+/');
$plainText = base64_decode($base64);
return ($plainText);
}
?>
I had some trouble trying to let base64_decode decode base64-strings longer than ~5k chars.
The base64-decoding function is a homomorphism between modulo 4 and modulo 3-length segmented strings. That motivates a divide and conquer approach: Split the encoded string into substrings counting modulo 4 chars, then decode each substring and concatenate all of them.
Then instead of
<?php $decoded = base64_decode($encoded); ?>
for big $encoded strings, it's saver to use
<?php
$decoded = "";
for ($i=0; $i < ceil(strlen($encoded)/256); $i++)
$decoded = $decoded . base64_decode(substr($encoded,$i*256,256));
?>
where 256 can be replaced by a sufficiently small modulo 4 natural.
If you want to save data that is derived from a Javascript canvas.toDataURL() function, you have to convert blanks into plusses. If you do not do that, the decoded data is corrupted:
<?php
$encodedData = str_replace(' ','+',$encodedData);
$decocedData = base64_decode($encodedData);
?>
Base64 for URL parameters/filenames, that adhere to RFC 4648.
Defaults to dropping the padding on encode since it's not required for decoding, and keeps the URL free of % encodings.
<?php
function base64url_encode($data, $pad = null) {
$data = str_replace(array('+', '/'), array('-', '_'), base64_encode($data));
if (!$pad) {
$data = rtrim($data, '=');
}
return $data;
}
function base64url_decode($data) {
return base64_decode(str_replace(array('-', '_'), array('+', '/'), $data));
}
function is_base64($str){
if($str === base64_encode(base64_decode($str))){
return true;
}
return false;
}
---------------------------------------------------------------------------
---------------------------------------------------------------------------
---------------------------------------------------------------------------
$str = 'VGhpcyBpcyBiYXNlNjQgZW5jb2RlIHN0cmluZw==';
if(is_base64($str)){
print base64_decode($str);
}
Note, that padding characters are not limited to "=". any character(s) at the end of the string that cannot be decoded will be interpreted as padding. if $strict is set to true, of course padding characters are limited to base64 characters.
examples:
<?php
// $strict = false;
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw==';
echo base64_decode($str); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw';
echo base64_decode($str); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZwA';
echo base64_decode($str); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZwA=';
echo base64_decode($str); // This is an encoded string
// $strict = true;
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw==';
echo base64_decode($str, true); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw';
echo base64_decode($str, true); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZwA';
echo base64_decode($str, true); // This is an encoded string
$str = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZwA=';
echo base64_decode($str, true); // This is an encoded string
?>