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    base64_decode

    (PHP 4, PHP 5, PHP 7, PHP 8)

    base64_decode — MIME base64 方式によりエンコードされたデータをデコードする

    説明

    base64_decode(string $string, bool $strict = false): string|false

    base64 でエンコードされた string をデコードします。

    パラメータ

    string

    デコードされるデータ。

    strict

    strict パラメータを true に指定すると、 base64_decode() 関数は、 入力に base64 アルファベットの範囲外の文字が含まれる場合に false を返します。 それ以外の場合は、base64 アルファベットの範囲外の文字を破棄したうえでデコードされます。

    戻り値

    デコードされたデータを返します。失敗した場合に false を返します。 戻り値はバイナリになることもあります。

    例

    例1 base64_decode() の例

    <?php
    $str     = 'VGhpcyBpcyBhbiBlbmNvZGVkIHN0cmluZw==';
    echo     base64_decode($str);
    ?>

    上の例の出力は以下となります。

    This is an encoded string

    参考

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    User Contributed Notes 6 notes

    up
    76
    winkelnkemper at googlemail dot com
    13 years ago
    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);
    ?>
    up
    3
    martinstaemmler at gmx dot net
    15 years ago
    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.
    up
    0
    pete panic
    11 months ago
    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
    ?>
    up
    2
    Tom
    18 years ago
    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);
    }
    ?>
    up
    0
    walf
    9 years ago
    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('+', '/'), $data));
    }
    up
    -5
    user at sfdsfd dot com
    5 years ago
    function is_base64($str){
    if($str === base64_encode(base64_decode($str))){
    return true;
    }
    return false;
    }

    ---------------------------------------------------------------------------
    ---------------------------------------------------------------------------
    ---------------------------------------------------------------------------

    $str = 'VGhpcyBpcyBiYXNlNjQgZW5jb2RlIHN0cmluZw==';

    if(is_base64($str)){
    print base64_decode($str);
    }
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