C++中的BASE64解码片段

这是我对 the implementation that was originally written by René Nyffenegger std::string 对象;)

:

#ifndef _BASE64_H_
#define _BASE64_H_

#include <vector>
#include <string>
typedef unsigned char BYTE;

std::string base64_encode(BYTE const* buf, unsigned int bufLen);
std::vector<BYTE> base64_decode(std::string const&);

#endif

:

#include "base64.h"
#include <iostream>

static const std::string base64_chars =
             "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
             "abcdefghijklmnopqrstuvwxyz"
             "0123456789+/";


static inline bool is_base64(BYTE c) {
  return (isalnum(c) || (c == '+') || (c == '/'));
}

std::string base64_encode(BYTE const* buf, unsigned int bufLen) {
  std::string ret;
  int i = 0;
  int j = 0;
  BYTE char_array_3[3];
  BYTE char_array_4[4];

  while (bufLen--) {
    char_array_3[i++] = *(buf++);
    if (i == 3) {
      char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
      char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
      char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
      char_array_4[3] = char_array_3[2] & 0x3f;

      for(i = 0; (i <4) ; i++)
        ret += base64_chars[char_array_4[i]];
      i = 0;
    }
  }

  if (i)
  {
    for(j = i; j < 3; j++)
      char_array_3[j] = '\0';

    char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
    char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
    char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
    char_array_4[3] = char_array_3[2] & 0x3f;

    for (j = 0; (j < i + 1); j++)
      ret += base64_chars[char_array_4[j]];

    while((i++ < 3))
      ret += '=';
  }

  return ret;
}

std::vector<BYTE> base64_decode(std::string const& encoded_string) {
  int in_len = encoded_string.size();
  int i = 0;
  int j = 0;
  int in_ = 0;
  BYTE char_array_4[4], char_array_3[3];
  std::vector<BYTE> ret;

  while (in_len-- && ( encoded_string[in_] != '=') && is_base64(encoded_string[in_])) {
    char_array_4[i++] = encoded_string[in_]; in_++;
    if (i ==4) {
      for (i = 0; i <4; i++)
        char_array_4[i] = base64_chars.find(char_array_4[i]);

      char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
      char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
      char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];

      for (i = 0; (i < 3); i++)
          ret.push_back(char_array_3[i]);
      i = 0;
    }
  }

  if (i) {
    for (j = i; j <4; j++)
      char_array_4[j] = 0;

    for (j = 0; j <4; j++)
      char_array_4[j] = base64_chars.find(char_array_4[j]);

    char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
    char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
    char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];

    for (j = 0; (j < i - 1); j++) ret.push_back(char_array_3[j]);
  }

  return ret;
}

std::vector<BYTE> myData;
...
std::string encodedData = base64_encode(&myData[0], myData.size());
std::vector<BYTE> decodedData = base64_decode(encodedData);

看见 Encoding and decoding base 64 with C++

以下是该页面的实现:

/*
   base64.cpp and base64.h

   Copyright (C) 2004-2008 René Nyffenegger

   This source code is provided 'as-is', without any express or implied
   warranty. In no event will the author be held liable for any damages
   arising from the use of this software.

   Permission is granted to anyone to use this software for any purpose,
   including commercial applications, and to alter it and redistribute it
   freely, subject to the following restrictions:

   1. The origin of this source code must not be misrepresented; you must not
      claim that you wrote the original source code. If you use this source code
      in a product, an acknowledgment in the product documentation would be
      appreciated but is not required.

   2. Altered source versions must be plainly marked as such, and must not be
      misrepresented as being the original source code.

   3. This notice may not be removed or altered from any source distribution.

   René Nyffenegger rene.nyffenegger@adp-gmbh.ch

*/

static const std::string base64_chars =
             "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
             "abcdefghijklmnopqrstuvwxyz"
             "0123456789+/";


static inline bool is_base64(unsigned char c) {
  return (isalnum(c) || (c == '+') || (c == '/'));
}

std::string base64_encode(unsigned char const* bytes_to_encode, unsigned int in_len) {
  std::string ret;
  int i = 0;
  int j = 0;
  unsigned char char_array_3[3];
  unsigned char char_array_4[4];

  while (in_len--) {
    char_array_3[i++] = *(bytes_to_encode++);
    if (i == 3) {
      char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
      char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
      char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
      char_array_4[3] = char_array_3[2] & 0x3f;

      for(i = 0; (i <4) ; i++)
        ret += base64_chars[char_array_4[i]];
      i = 0;
    }
  }

  if (i)
  {
    for(j = i; j < 3; j++)
      char_array_3[j] = '\0';

    char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
    char_array_4[1] = ((char_array_3[0] & 0x03) << 4) + ((char_array_3[1] & 0xf0) >> 4);
    char_array_4[2] = ((char_array_3[1] & 0x0f) << 2) + ((char_array_3[2] & 0xc0) >> 6);
    char_array_4[3] = char_array_3[2] & 0x3f;

    for (j = 0; (j < i + 1); j++)
      ret += base64_chars[char_array_4[j]];

    while((i++ < 3))
      ret += '=';

  }

  return ret;

}
std::string base64_decode(std::string const& encoded_string) {
  int in_len = encoded_string.size();
  int i = 0;
  int j = 0;
  int in_ = 0;
  unsigned char char_array_4[4], char_array_3[3];
  std::string ret;

  while (in_len-- && ( encoded_string[in_] != '=') && is_base64(encoded_string[in_])) {
    char_array_4[i++] = encoded_string[in_]; in_++;
    if (i ==4) {
      for (i = 0; i <4; i++)
        char_array_4[i] = base64_chars.find(char_array_4[i]);

      char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
      char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
      char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];

      for (i = 0; (i < 3); i++)
        ret += char_array_3[i];
      i = 0;
    }
  }

  if (i) {
    for (j = i; j <4; j++)
      char_array_4[j] = 0;

    for (j = 0; j <4; j++)
      char_array_4[j] = base64_chars.find(char_array_4[j]);

    char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
    char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
    char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];

    for (j = 0; (j < i - 1); j++) ret += char_array_3[j];
  }

  return ret;
}

这里有几个片段。但是,这是一款紧凑、高效且对C++11友好的产品:

static std::string base64_encode(const std::string &in) {

    std::string out;

    int val = 0, valb = -6;
    for (uchar c : in) {
        val = (val << 8) + c;
        valb += 8;
        while (valb >= 0) {
            out.push_back("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"[(val>>valb)&0x3F]);
            valb -= 6;
        }
    }
    if (valb>-6) out.push_back("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"[((val<<8)>>(valb+8))&0x3F]);
    while (out.size()%4) out.push_back('=');
    return out;
}

static std::string base64_decode(const std::string &in) {

    std::string out;

    std::vector<int> T(256,-1);
    for (int i=0; i<64; i++) T["ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"[i]] = i;

    int val=0, valb=-8;
    for (uchar c : in) {
        if (T[c] == -1) break;
        val = (val << 6) + T[c];
        valb += 6;
        if (valb >= 0) {
            out.push_back(char((val>>valb)&0xFF));
            valb -= 8;
        }
    }
    return out;
}

我认为这个更好:

#include <string>

static const char* B64chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

static const int B64index[256] =
{
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  62, 63, 62, 62, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 0,  0,  0,  0,  0,  0,
    0,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10, 11, 12, 13, 14,
    15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 0,  0,  0,  0,  63,
    0,  26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
    41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51
};

const std::string b64encode(const void* data, const size_t &len)
{
    std::string result((len + 2) / 3 * 4, '=');
    unsigned char *p = (unsigned  char*) data;
    char *str = &result[0];
    size_t j = 0, pad = len % 3;
    const size_t last = len - pad;

    for (size_t i = 0; i < last; i += 3)
    {
        int n = int(p[i]) << 16 | int(p[i + 1]) << 8 | p[i + 2];
        str[j++] = B64chars[n >> 18];
        str[j++] = B64chars[n >> 12 & 0x3F];
        str[j++] = B64chars[n >> 6 & 0x3F];
        str[j++] = B64chars[n & 0x3F];
    }
    if (pad)  /// Set padding
    {
        int n = --pad ? int(p[last]) << 8 | p[last + 1] : p[last];
        str[j++] = B64chars[pad ? n >> 10 & 0x3F : n >> 2];
        str[j++] = B64chars[pad ? n >> 4 & 0x03F : n << 4 & 0x3F];
        str[j++] = pad ? B64chars[n << 2 & 0x3F] : '=';
    }
    return result;
}

const std::string b64decode(const void* data, const size_t &len)
{
    if (len == 0) return "";

    unsigned char *p = (unsigned char*) data;
    size_t j = 0,
        pad1 = len % 4 || p[len - 1] == '=',
        pad2 = pad1 && (len % 4 > 2 || p[len - 2] != '=');
    const size_t last = (len - pad1) / 4 << 2;
    std::string result(last / 4 * 3 + pad1 + pad2, '\0');
    unsigned char *str = (unsigned char*) &result[0];

    for (size_t i = 0; i < last; i += 4)
    {
        int n = B64index[p[i]] << 18 | B64index[p[i + 1]] << 12 | B64index[p[i + 2]] << 6 | B64index[p[i + 3]];
        str[j++] = n >> 16;
        str[j++] = n >> 8 & 0xFF;
        str[j++] = n & 0xFF;
    }
    if (pad1)
    {
        int n = B64index[p[last]] << 18 | B64index[p[last + 1]] << 12;
        str[j++] = n >> 16;
        if (pad2)
        {
            n |= B64index[p[last + 2]] << 6;
            str[j++] = n >> 8 & 0xFF;
        }
    }
    return result;
}

std::string b64encode(const std::string& str)
{
    return b64encode(str.c_str(), str.size());
}

std::string b64decode(const std::string& str64)
{
    return b64decode(str64.c_str(), str64.size());
}

幸亏 Jens Alfke for pointing out a performance issue 古老的 邮递这个比以前快多了。它的另一个优点是能够顺利处理损坏的数据。

当前位置虽然在这类问题中,速度似乎是一种过激的手段,但为了好玩,我做了一些其他的修改,使之成为目前最快的算法。特别感谢 GaspardP for his valuable suggestions 很好的基准。

使用 base-n 迷你库,您可以执行以下操作:

some_data_t in[] { ... };
constexpr int len = sizeof(in)/sizeof(in[0]);

std::string encoded;
bn::encode_b64(in, in + len, std::back_inserter(encoded));

some_data_t out[len];
bn::decode_b64(encoded.begin(), encoded.end(), out);

披露:我是作者。

根据 this excellent comparison

我发现另外两个答案很难理解。它们还会在我的编译器中产生一些警告,在解码部分使用find函数会导致相当糟糕的效率。所以我决定自己动手。

标题:

#ifndef _BASE64_H_
#define _BASE64_H_

#include <vector>
#include <string>
typedef unsigned char BYTE;

class Base64
{
public:
    static std::string encode(const std::vector<BYTE>& buf);
    static std::string encode(const BYTE* buf, unsigned int bufLen);
    static std::vector<BYTE> decode(std::string encoded_string);
};

#endif

static const BYTE from_base64[] = {    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
                                    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
                                    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,  62, 255,  62, 255,  63,
                                     52,  53,  54,  55,  56,  57,  58,  59,  60,  61, 255, 255, 255, 255, 255, 255,
                                    255,   0,   1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,
                                     15,  16,  17,  18,  19,  20,  21,  22,  23,  24,  25, 255, 255, 255, 255,  63,
                                    255,  26,  27,  28,  29,  30,  31,  32,  33,  34,  35,  36,  37,  38,  39,  40,
                                     41,  42,  43,  44,  45,  46,  47,  48,  49,  50,  51, 255, 255, 255, 255, 255};

static const char to_base64[] =
             "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
             "abcdefghijklmnopqrstuvwxyz"
             "0123456789+/";


std::string Base64::encode(const std::vector<BYTE>& buf)
{
    if (buf.empty())
        return ""; // Avoid dereferencing buf if it's empty
    return encode(&buf[0], (unsigned int)buf.size());
}

std::string Base64::encode(const BYTE* buf, unsigned int bufLen)
{
    // Calculate how many bytes that needs to be added to get a multiple of 3
    size_t missing = 0;
    size_t ret_size = bufLen;
    while ((ret_size % 3) != 0)
    {
        ++ret_size;
        ++missing;
    }

    // Expand the return string size to a multiple of 4
    ret_size = 4*ret_size/3;

    std::string ret;
    ret.reserve(ret_size);

    for (unsigned int i=0; i<ret_size/4; ++i)
    {
        // Read a group of three bytes (avoid buffer overrun by replacing with 0)
        size_t index = i*3;
        BYTE b3[3];
        b3[0] = (index+0 < bufLen) ? buf[index+0] : 0;
        b3[1] = (index+1 < bufLen) ? buf[index+1] : 0;
        b3[2] = (index+2 < bufLen) ? buf[index+2] : 0;

        // Transform into four base 64 characters
        BYTE b4[4];
        b4[0] =                            ((b3[0] & 0xfc) >> 2);
        b4[1] = ((b3[0] & 0x03) << 4) +    ((b3[1] & 0xf0) >> 4);
        b4[2] = ((b3[1] & 0x0f) << 2) +    ((b3[2] & 0xc0) >> 6);
        b4[3] = ((b3[2] & 0x3f) << 0);

        // Add the base 64 characters to the return value
        ret.push_back(to_base64[b4[0]]);
        ret.push_back(to_base64[b4[1]]);
        ret.push_back(to_base64[b4[2]]);
        ret.push_back(to_base64[b4[3]]);
    }

    // Replace data that is invalid (always as many as there are missing bytes)
    for (size_t i=0; i<missing; ++i)
        ret[ret_size - i - 1] = '=';

    return ret;
}

std::vector<BYTE> Base64::decode(std::string encoded_string)
{
    // Make sure string length is a multiple of 4
    while ((encoded_string.size() % 4) != 0)
        encoded_string.push_back('=');

    size_t encoded_size = encoded_string.size();
    std::vector<BYTE> ret;
    ret.reserve(3*encoded_size/4);

    for (size_t i=0; i<encoded_size; i += 4)
    {
        // Get values for each group of four base 64 characters
        BYTE b4[4];
        b4[0] = (encoded_string[i+0] <= 'z') ? from_base64[encoded_string[i+0]] : 0xff;
        b4[1] = (encoded_string[i+1] <= 'z') ? from_base64[encoded_string[i+1]] : 0xff;
        b4[2] = (encoded_string[i+2] <= 'z') ? from_base64[encoded_string[i+2]] : 0xff;
        b4[3] = (encoded_string[i+3] <= 'z') ? from_base64[encoded_string[i+3]] : 0xff;

        // Transform into a group of three bytes
        BYTE b3[3];
        b3[0] = ((b4[0] & 0x3f) << 2) + ((b4[1] & 0x30) >> 4);
        b3[1] = ((b4[1] & 0x0f) << 4) + ((b4[2] & 0x3c) >> 2);
        b3[2] = ((b4[2] & 0x03) << 6) + ((b4[3] & 0x3f) >> 0);

        // Add the byte to the return value if it isn't part of an '=' character (indicated by 0xff)
        if (b4[1] != 0xff) ret.push_back(b3[0]);
        if (b4[2] != 0xff) ret.push_back(b3[1]);
        if (b4[3] != 0xff) ret.push_back(b3[2]);
    }

    return ret;
}

用法:

BYTE buf[] = "ABCD";
std::string encoded = Base64::encode(buf, 4);
// encoded = "QUJDRA=="
std::vector<BYTE> decoded = Base64::decode(encoded);

这里的一个好处是decode函数还可以解码Base64编码的URL变量。

更紧凑的查找表和使用C++17功能的一些变化:

std::string base64_decode(const std::string_view in) {
  // table from '+' to 'z'
  const uint8_t lookup[] = {
      62,  255, 62,  255, 63,  52,  53, 54, 55, 56, 57, 58, 59, 60, 61, 255,
      255, 0,   255, 255, 255, 255, 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,
      10,  11,  12,  13,  14,  15,  16, 17, 18, 19, 20, 21, 22, 23, 24, 25,
      255, 255, 255, 255, 63,  255, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,
      36,  37,  38,  39,  40,  41,  42, 43, 44, 45, 46, 47, 48, 49, 50, 51};
  static_assert(sizeof(lookup) == 'z' - '+' + 1);

  std::string out;
  int val = 0, valb = -8;
  for (uint8_t c : in) {
    if (c < '+' || c > 'z')
      break;
    c -= '+';
    if (lookup[c] >= 64)
      break;
    val = (val << 6) + lookup[c];
    valb += 6;
    if (valb >= 0) {
      out.push_back(char((val >> valb) & 0xFF));
      valb -= 8;
    }
  }
  return out;
}

我的变化 DaedalusAlpha's answer :

为处理字符串添加了一些方便的函数,尽管输入数据通常是二进制的,并且内部可能没有字节,因此通常不应作为字符串进行操作(这通常意味着以null结尾的数据)。

还添加了一些强制转换来修复编译器警告(至少在GCC上,我还没有通过MSVC运行它)。

base64.hpp :

void base64_encode(string & out, const vector<uint8_t>& buf);
void base64_encode(string & out, const uint8_t* buf, size_t bufLen);
void base64_encode(string & out, string const& buf);

void base64_decode(vector<uint8_t> & out, string const& encoded_string);

// Use this if you know the output should be a valid string
void base64_decode(string & out, string const& encoded_string);

文件

static const uint8_t from_base64[128] = {
    // 8 rows of 16 = 128
    // Note: only requires 123 entries, as we only lookup for <= z , which z=122

    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,  62, 255,  62, 255,  63,
     52,  53,  54,  55,  56,  57,  58,  59,  60,  61, 255, 255,   0, 255, 255, 255,
    255,   0,   1,   2,   3,   4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,
     15,  16,  17,  18,  19,  20,  21,  22,  23,  24,  25, 255, 255, 255, 255,  63,
    255,  26,  27,  28,  29,  30,  31,  32,  33,  34,  35,  36,  37,  38,  39,  40,
     41,  42,  43,  44,  45,  46,  47,  48,  49,  50,  51, 255, 255, 255, 255, 255
};

static const char to_base64[65] =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "abcdefghijklmnopqrstuvwxyz"
    "0123456789+/";


void base64_encode(string & out, string const& buf)
{
   if (buf.empty())
      base64_encode(out, NULL, 0);
   else
      base64_encode(out, reinterpret_cast<uint8_t const*>(&buf[0]), buf.size());
}


void base64_encode(string & out, std::vector<uint8_t> const& buf)
{
   if (buf.empty())
      base64_encode(out, NULL, 0);
   else
      base64_encode(out, &buf[0], buf.size());
}

void base64_encode(string & ret, uint8_t const* buf, size_t bufLen)
{
   // Calculate how many bytes that needs to be added to get a multiple of 3
   size_t missing = 0;
   size_t ret_size = bufLen;
   while ((ret_size % 3) != 0)
   {
      ++ret_size;
      ++missing;
   }

   // Expand the return string size to a multiple of 4
   ret_size = 4*ret_size/3;

   ret.clear();
   ret.reserve(ret_size);

   for (size_t i = 0; i < ret_size/4; ++i)
   {
      // Read a group of three bytes (avoid buffer overrun by replacing with 0)
      const size_t index = i*3;
      const uint8_t b3_0 = (index+0 < bufLen) ? buf[index+0] : 0;
      const uint8_t b3_1 = (index+1 < bufLen) ? buf[index+1] : 0;
      const uint8_t b3_2 = (index+2 < bufLen) ? buf[index+2] : 0;

      // Transform into four base 64 characters
      const uint8_t b4_0 =                        ((b3_0 & 0xfc) >> 2);
      const uint8_t b4_1 = ((b3_0 & 0x03) << 4) + ((b3_1 & 0xf0) >> 4);
      const uint8_t b4_2 = ((b3_1 & 0x0f) << 2) + ((b3_2 & 0xc0) >> 6);
      const uint8_t b4_3 = ((b3_2 & 0x3f) << 0);

      // Add the base 64 characters to the return value
      ret.push_back(to_base64[b4_0]);
      ret.push_back(to_base64[b4_1]);
      ret.push_back(to_base64[b4_2]);
      ret.push_back(to_base64[b4_3]);
   }

   // Replace data that is invalid (always as many as there are missing bytes)
   for (size_t i = 0; i != missing; ++i)
      ret[ret_size - i - 1] = '=';
}


template <class Out>
void base64_decode_any( Out & ret, std::string const& in)
{
   typedef typename Out::value_type T;

   // Make sure the *intended* string length is a multiple of 4
   size_t encoded_size = in.size();

   while ((encoded_size % 4) != 0)
      ++encoded_size;

   const size_t N = in.size();
   ret.clear();
   ret.reserve(3*encoded_size/4);

   for (size_t i = 0; i < encoded_size; i += 4)
   {
      // Note: 'z' == 122

      // Get values for each group of four base 64 characters
      const uint8_t b4_0 = (            in[i+0] <= 'z') ? from_base64[static_cast<uint8_t>(in[i+0])] : 0xff;
      const uint8_t b4_1 = (i+1 < N and in[i+1] <= 'z') ? from_base64[static_cast<uint8_t>(in[i+1])] : 0xff;
      const uint8_t b4_2 = (i+2 < N and in[i+2] <= 'z') ? from_base64[static_cast<uint8_t>(in[i+2])] : 0xff;
      const uint8_t b4_3 = (i+3 < N and in[i+3] <= 'z') ? from_base64[static_cast<uint8_t>(in[i+3])] : 0xff;

      // Transform into a group of three bytes
      const uint8_t b3_0 = ((b4_0 & 0x3f) << 2) + ((b4_1 & 0x30) >> 4);
      const uint8_t b3_1 = ((b4_1 & 0x0f) << 4) + ((b4_2 & 0x3c) >> 2);
      const uint8_t b3_2 = ((b4_2 & 0x03) << 6) + ((b4_3 & 0x3f) >> 0);

      // Add the byte to the return value if it isn't part of an '=' character (indicated by 0xff)
      if (b4_1 != 0xff) ret.push_back( static_cast<T>(b3_0) );
      if (b4_2 != 0xff) ret.push_back( static_cast<T>(b3_1) );
      if (b4_3 != 0xff) ret.push_back( static_cast<T>(b3_2) );
   }
}

void base64_decode(vector<uint8_t> & out, string const& encoded_string)
{
   base64_decode_any(out, encoded_string);
}

void base64_decode(string & out, string const& encoded_string)
{
   base64_decode_any(out, encoded_string);
}

我的版本是用于C++Builder的Base64的简单快速编码器(解码器)。

// ---------------------------------------------------------------------------
UnicodeString __fastcall TExample::Base64Encode(void *data, int length)
{
    if (length <= 0)
        return L"";
    static const char set[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    unsigned char *in = (unsigned char*)data;
    char *pos, *out = pos = new char[((length - 1) / 3 + 1) << 2];
    while ((length -= 3) >= 0)
    {
        pos[0] = set[in[0] >> 2];
        pos[1] = set[((in[0] & 0x03) << 4) | (in[1] >> 4)];
        pos[2] = set[((in[1] & 0x0F) << 2) | (in[2] >> 6)];
        pos[3] = set[in[2] & 0x3F];
        pos += 4;
        in += 3;
    };
    if ((length & 2) != 0)
    {
        pos[0] = set[in[0] >> 2];
        if ((length & 1) != 0)
        {
            pos[1] = set[((in[0] & 0x03) << 4) | (in[1] >> 4)];
            pos[2] = set[(in[1] & 0x0F) << 2];
        }
        else
        {
            pos[1] = set[(in[0] & 0x03) << 4];
            pos[2] = '=';
        };
        pos[3] = '=';
        pos += 4;
    };
    UnicodeString code = UnicodeString(out, pos - out);
    delete[] out;
    return code;
};

// ---------------------------------------------------------------------------
int __fastcall TExample::Base64Decode(const UnicodeString &code, unsigned char **data)
{
    int length;
    if (((length = code.Length()) == 0) || ((length & 3) != 0))
        return 0;
    wchar_t *str = code.c_str();
    unsigned char *pos, *out = pos = new unsigned char[(length >> 2) * 3];
    while (*str != 0)
    {
        length = -1;
        int shift = 18, bits = 0;
        do
        {
            wchar_t s = str[++length];
            if ((s >= L'A') && (s <= L'Z'))
                bits |= (s - L'A') << shift;
            else if ((s >= L'a') && (s <= L'z'))
                   bits |= (s - (L'a' - 26)) << shift;
            else if (((s >= L'0') && (s <= L'9')))
                   bits |= (s - (L'0' - 52)) << shift;
            else if (s == L'+')
                   bits |= 62 << shift;
            else if (s == L'/')
                   bits |= 63 << shift;
            else if (s == L'=')
            {
                length--;
                break;
            }
            else
            {
                delete[] out;
                return 0;
            };
        }
        while ((shift -= 6) >= 0);
        pos[0] = bits >> 16;
        pos[1] = bits >> 8;
        pos[2] = bits;
        pos += length;
        str += 4;
    };
    *data = out;
    return pos - out;
};
//---------------------------------------------------------------------------

class BinaryVector {
public:
    std::vector<char> bytes;

    uint64_t bit_count = 0;

public:
    /* Add a bit to the end */
    void push_back(bool bit);

    /* Return false if character is unrecognized */
    bool pushBase64Char(char b64_c);
};

void BinaryVector::push_back(bool bit)
{
    if (!bit_count || bit_count % 8 == 0) {
        bytes.push_back(bit << 7);
    }
    else {
        uint8_t next_bit = 8 - (bit_count % 8) - 1;
        bytes[bit_count / 8] |= bit << next_bit;
    }
    bit_count++;
}

/* Converts one Base64 character to 6 bits */
bool BinaryVector::pushBase64Char(char c)
{
    uint8_t d;

    // A to Z
    if (c > 0x40 && c < 0x5b) {
        d = c - 65;  // Base64 A is 0
    }
    // a to z
    else if (c > 0x60 && c < 0x7b) {
        d = c - 97 + 26;  // Base64 a is 26
    }
    // 0 to 9
    else if (c > 0x2F && c < 0x3a) {
        d = c - 48 + 52;  // Base64 0 is 52
    }
    else if (c == '+') {
        d = 0b111110;
    }
    else if (c == '/') {
        d = 0b111111;
    }
    else if (c == '=') {
        d = 0;
    }
    else {
        return false;
    }

    push_back(d & 0b100000);
    push_back(d & 0b010000);
    push_back(d & 0b001000);
    push_back(d & 0b000100);
    push_back(d & 0b000010);
    push_back(d & 0b000001);

    return true;
}

bool loadBase64(std::vector<char>& b64_bin, BinaryVector& vec)
{
    for (char& c : b64_bin) {
        if (!vec.pushBase64Char(c)) {
            return false;
        }
    }
    return true;
}

使用 vec.bytes 访问转换后的数据。

为什么我的版本看起来比这里介绍的其他版本更简单?我做错什么了吗?我没有测试它的速度。

inline char const* b64units = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

inline char* b64encode(void const* a, int64_t b) {
    ASSERT(a != nullptr);
    if (b > 0) {
        uint8_t const* aa = static_cast<uint8_t const*>(a);
        uint8_t v = 0;
        int64_t bp = 0;
        int64_t sb = 0;
        int8_t off = 0;
        int64_t nt = ((b + 2) / 3) * 4;
        int64_t nd = (b * 8) / 6;
        int64_t tl = ((b * 8) % 6) ? 1 : 0;
        int64_t nf = nt - nd - tl;
        int64_t ri = 0;
        char* r = new char[nt + 1]();
        for (int64_t i = 0; i < nd; i++) {
            v = (aa[sb] << off) | (aa[sb + 1] >> (8 - off));
            v >>= 2;
            r[ri] = b64units[v];
            ri += 1;
            bp += 6;
            sb = (bp / 8);
            off = (bp % 8);
        }
        if (tl > 0) {
            v = (aa[sb] << off);
            v >>= 2;
            r[ri] = b64units[v];
            ri += 1;
        }
        for (int64_t i = 0; i < nf; i++) {
            r[ri] = '=';
            ri += 1;
        }
        return r;
    } else return nullptr;
}

附言:我的方法很有效。我试了一下 Node.js :

let data = 'stackabuse.com';
let buff = new Buffer(data);
let base64data = buff.toString('base64');

我喜欢 this solution on GitHub

它是单个hpp文件,使用向量<字节>输入原始数据,而不是接受的答案。

#pragma once

#include <string>
#include <vector>
#include <stdexcept>
#include <cstdint>

namespace base64
{
    inline static const char kEncodeLookup[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    inline static const char kPadCharacter = '=';

    using byte = std::uint8_t;

    inline std::string encode(const std::vector<byte>& input)
    {
        std::string encoded;
        encoded.reserve(((input.size() / 3) + (input.size() % 3 > 0)) * 4);

        std::uint32_t temp{};
        auto it = input.begin();

        for(std::size_t i = 0; i < input.size() / 3; ++i)
        {
            temp  = (*it++) << 16;
            temp += (*it++) << 8;
            temp += (*it++);
            encoded.append(1, kEncodeLookup[(temp & 0x00FC0000) >> 18]);
            encoded.append(1, kEncodeLookup[(temp & 0x0003F000) >> 12]);
            encoded.append(1, kEncodeLookup[(temp & 0x00000FC0) >> 6 ]);
            encoded.append(1, kEncodeLookup[(temp & 0x0000003F)      ]);
        }

        switch(input.size() % 3)
        {
        case 1:
            temp = (*it++) << 16;
            encoded.append(1, kEncodeLookup[(temp & 0x00FC0000) >> 18]);
            encoded.append(1, kEncodeLookup[(temp & 0x0003F000) >> 12]);
            encoded.append(2, kPadCharacter);
            break;
        case 2:
            temp  = (*it++) << 16;
            temp += (*it++) << 8;
            encoded.append(1, kEncodeLookup[(temp & 0x00FC0000) >> 18]);
            encoded.append(1, kEncodeLookup[(temp & 0x0003F000) >> 12]);
            encoded.append(1, kEncodeLookup[(temp & 0x00000FC0) >> 6 ]);
            encoded.append(1, kPadCharacter);
            break;
        }

        return encoded;
    }

    std::vector<byte> decode(const std::string& input)
    {
        if(input.length() % 4)
            throw std::runtime_error("Invalid base64 length!");

        std::size_t padding{};

        if(input.length())
        {
            if(input[input.length() - 1] == kPadCharacter) padding++;
            if(input[input.length() - 2] == kPadCharacter) padding++;
        }

        std::vector<byte> decoded;
        decoded.reserve(((input.length() / 4) * 3) - padding);

        std::uint32_t temp{};
        auto it = input.begin();

        while(it < input.end())
        {
            for(std::size_t i = 0; i < 4; ++i)
            {
                temp <<= 6;
                if     (*it >= 0x41 && *it <= 0x5A) temp |= *it - 0x41;
                else if(*it >= 0x61 && *it <= 0x7A) temp |= *it - 0x47;
                else if(*it >= 0x30 && *it <= 0x39) temp |= *it + 0x04;
                else if(*it == 0x2B)                temp |= 0x3E;
                else if(*it == 0x2F)                temp |= 0x3F;
                else if(*it == kPadCharacter)
                {
                    switch(input.end() - it)
                    {
                    case 1:
                        decoded.push_back((temp >> 16) & 0x000000FF);
                        decoded.push_back((temp >> 8 ) & 0x000000FF);
                        return decoded;
                    case 2:
                        decoded.push_back((temp >> 10) & 0x000000FF);
                        return decoded;
                    default:
                        throw std::runtime_error("Invalid padding in base64!");
                    }
                }
                else throw std::runtime_error("Invalid character in base64!");

                ++it;
            }

            decoded.push_back((temp >> 16) & 0x000000FF);
            decoded.push_back((temp >> 8 ) & 0x000000FF);
            decoded.push_back((temp      ) & 0x000000FF);
        }

        return decoded;
    }
}

const char PADDING_CHAR = '=';
const char* ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
const uint8_t DECODED_ALPHBET[128]={0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,62,0,0,0,63,52,53,54,55,56,57,58,59,60,61,0,0,0,0,0,0,0,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,0,0,0,0,0,0,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,0,0,0,0,0};

/**
 * Given a string, this function will encode it in 64b (with padding)
 */
std::string encodeBase64(const std::string& binaryText)
{
    std::string encoded((binaryText.size()/3 + (binaryText.size()%3 > 0)) << 2, PADDING_CHAR);

    const char* bytes = binaryText.data();
    union
    {
        uint32_t temp = 0;
        struct
        {
            uint32_t first : 6, second : 6, third : 6, fourth : 6;
        } tempBytes;
    };
    std::string::iterator currEncoding = encoded.begin();

    for(uint32_t i = 0, lim = binaryText.size() / 3; i < lim; ++i, bytes+=3)
    {
        temp = bytes[0] << 16 | bytes[1] << 8 | bytes[2];
        (*currEncoding++) = ALPHABET[tempBytes.fourth];
        (*currEncoding++) = ALPHABET[tempBytes.third];
        (*currEncoding++) = ALPHABET[tempBytes.second];
        (*currEncoding++) = ALPHABET[tempBytes.first];
    }

    switch(binaryText.size() % 3)
    {
    case 1:
        temp = bytes[0] << 16;
        (*currEncoding++) = ALPHABET[tempBytes.fourth];
        (*currEncoding++) = ALPHABET[tempBytes.third];
        break;
    case 2:
        temp = bytes[0] << 16 | bytes[1] << 8;
        (*currEncoding++) = ALPHABET[tempBytes.fourth];
        (*currEncoding++) = ALPHABET[tempBytes.third];
        (*currEncoding++) = ALPHABET[tempBytes.second];
        break;
    }

    return encoded;
}

/**
 * Given a 64b padding-encoded string, this function will decode it.
 */
std::string decodeBase64(const std::string& base64Text)
{
    if( base64Text.empty() )
        return "";

    assert((base64Text.size()&3) == 0 && "The base64 text to be decoded must have a length devisible by 4!");

    uint32_t numPadding =  (*std::prev(base64Text.end(),1) == PADDING_CHAR) + (*std::prev(base64Text.end(),2) == PADDING_CHAR);

    std::string decoded((base64Text.size()*3>>2) - numPadding, '.');

    union
    {
        uint32_t temp;
        char tempBytes[4];
    };
    const uint8_t* bytes = reinterpret_cast<const uint8_t*>(base64Text.data());

    std::string::iterator currDecoding = decoded.begin();

    for(uint32_t i = 0, lim = (base64Text.size() >> 2) - (numPadding!=0); i < lim; ++i, bytes+=4)
    {
        temp = DECODED_ALPHBET[bytes[0]] << 18 | DECODED_ALPHBET[bytes[1]] << 12 | DECODED_ALPHBET[bytes[2]] << 6 | DECODED_ALPHBET[bytes[3]];
        (*currDecoding++) = tempBytes[2];
        (*currDecoding++) = tempBytes[1];
        (*currDecoding++) = tempBytes[0];
    }

    switch (numPadding)
    {
    case 2:
        temp = DECODED_ALPHBET[bytes[0]] << 18 | DECODED_ALPHBET[bytes[1]] << 12;
        (*currDecoding++) = tempBytes[2];
        break;
    
    case 1:
        temp = DECODED_ALPHBET[bytes[0]] << 18 | DECODED_ALPHBET[bytes[1]] << 12 | DECODED_ALPHBET[bytes[2]] << 6;
        (*currDecoding++) = tempBytes[2];
        (*currDecoding++) = tempBytes[1];
        break;
    }

    return decoded;
}