C ++中的base64解码片段

base64 decode snippet in c++

提问by joeld

Anyone have a freely available base64 decoding code snippet in c++?

有人在 C++ 中有免费可用的 base64 解码代码片段吗？

回答by LihO

Here's my modification of the implementationthat was originally written by René Nyffenegger. And why have I modified it? Well, because it didn't seem appropriate to me that I should work with binary data stored within std::stringobject ;)

这是我对最初由René Nyffenegger编写的实现的修改。为什么我要修改它？好吧，因为我应该处理存储在对象中的二进制数据对我来说似乎不合适；)std::string

base64.h:

base64.h：

#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

base64.cpp:

base64.cpp:

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

    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;
}

Here's the usage:

这是用法：

/* 
   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 [email protected]

*/

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] = '
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;
}
';

    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;
}

I hope that someone will find this answer helpful ^^

我希望有人会发现这个答案有帮助^^

回答by John Millikin

Google is your friend

谷歌是你的朋友

Here is the implementation from that page:

这是该页面的实现：

#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, '=');
    char *p = (char*) data, *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, '
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);
');
    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());
}

回答by Manuel Martinez

There are several snippets here. However this one is compact, efficient, and c++11 friendly:

这里有几个片段。然而，这个是紧凑、高效且对 C++11 友好的：

#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

回答by polfosol ?_?

I think this one works better:

我认为这个效果更好：

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;
}

Thanks to @Jens Alfke for pointing out a performance issue, I have made some modifications to this oldpost. This one works way faster than before. Its other advantage is smooth handling of corrupt data as well.

感谢@Jens Alfke 指出了一个性能问题，我对这篇旧帖子做了一些修改。这个工作比以前快得多。它的另一个优点是可以顺利处理损坏的数据。

Last edition: Although in these kinds of problems, it seems that speed is an overkill, but just for the fun of it I have made some other modifications to make this one the fastest algorithm out there AFAIK. Special thanks goes to @GaspardP for his valuable suggestions and nice benchmark.

上一版：虽然在这些类型的问题中，速度似乎是一种矫枉过正，但只是为了好玩，我做了一些其他修改，使这个算法成为 AFAIK 中最快的算法。特别感谢@GaspardP 提出的宝贵建议和不错的基准测试。

回答by azawadzki

Using base-nmini lib, you can do the following:

使用base-n迷你库，您可以执行以下操作：

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

The API is generic, iterator-based.

API 是通用的、基于迭代器的。

Disclosure: I'm the author.

披露：我是作者。

回答by DaedalusAlpha

According to thisexcellent comparison made by GaspardP I would not choose this solution. It's not the worst, but it's not the best either. The only thing it got going for it is that it's possibly easier to understand.

根据这个由GaspardP我作了精彩比较不会选择这种解决方案。这不是最糟糕的，但也不是最好的。它唯一要做的就是它可能更容易理解。

I found the other two answers to be pretty hard to understand. They also produce some warnings in my compiler and the use of a find function in the decode part should result in a pretty bad efficiency. So I decided to roll my own.

我发现其他两个答案很难理解。它们还会在我的编译器中产生一些警告，并且在解码部分使用 find 函数会导致效率非常低。所以我决定自己动手。

Header:

标题：

   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);

Body:

身体：

static const uint8_t from_base64[128] = {
   // 8 rows of 16 = 128
   // note: only require 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);
}

Usage:

用法：

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;
}

A bonus here is that the decode function can also decode the url variant of base 64 encoding.

这里的一个好处是 decode 函数还可以解码 base 64 编码的 url 变体。

回答by elegant dice

My variation on @DaedalusAlpha answer. It avoids copying the parameters at the expense of a couple of tests.

我对@DaedalusAlpha 回答的变体。它避免了以几次测试为代价来复制参数。

Uses uint8_t instead of BYTE.

使用 uint8_t 而不是 BYTE。

Adds some handy functions for dealing with strings, although usually the input data is binary and may have zero bytes inside, so typically should not be manipulated as a string (which often implies null-terminated data).

添加了一些处理字符串的方便函数，尽管通常输入数据是二进制的并且内部可能有零字节，因此通常不应作为字符串进行操作（这通常意味着以空字符结尾的数据）。

Also adds some casts to fix compiler warnings (at least on GCC, I haven't run it through MSVC yet).

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）。

part of base64.hpp:

base64.hpp 的一部分：

//---------------------------------------------------------------------------
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;
};
//---------------------------------------------------------------------------

base64.cpp:

base64.cpp：

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;
}

回答by nunojpg

A little variation with a more compact lookup table and using c++17 features:

使用更紧凑的查找表和使用 c++17 功能的一些变化：

##代码##

If you don't have std::string_view try instead std::experimental::string_view.

如果您没有 std::string_view，请尝试使用 std::experimental::string_view。

回答by tutralex

My version is a simple fast encoder (decoder) of base64 for C++ Builder.

我的版本是用于 C++ Builder 的 base64 的简单快速编码器（解码器）。

##代码##

回答by Macelaru Tiberiu

My turn. I use this:

轮到我了。我用这个：

##代码##

Use vec.bytesto access converted data.

使用vec.bytes访问转换后的数据。