C++ 中是否有免费提供的 Base64 解码代码片段？
问问题
180033 次
13 回答
121
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？std::string好吧，因为对我来说，我应该使用存储在对象中的二进制数据似乎不合适；）
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：
#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;
}
这是用法：
std::vector<BYTE> myData;
...
std::string encodedData = base64_encode(&myData[0], myData.size());
std::vector<BYTE> decodedData = base64_decode(encodedData);
于 2012-12-18T15:02:52.980 回答
100
这是该页面的实现：
/*
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;
}
于 2008-10-08T00:28:35.443 回答
52
这里有几个片段。然而，这个是紧凑、高效且对 C++11 友好的：
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;
}
于 2016-01-02T21:51:25.433 回答
31
我认为这个效果更好：
#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());
}
感谢Jens Alfke 指出了性能问题，我对这篇旧帖子进行了一些修改。这个工作方式比以前更快。它的另一个优点是也可以顺利处理损坏的数据。
上一版：虽然在这类问题中，速度似乎有点过头了，但只是为了好玩，我做了一些其他修改，以使这个算法成为 AFAIK 中最快的算法。特别感谢GaspardP 的宝贵建议和良好的基准。
于 2016-05-09T06:41:34.930 回答
17
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);
API 是通用的，基于迭代器的。
披露：我是作者。
于 2014-08-04T16:13:23.137 回答
14
根据GaspardP 所做的出色比较，我不会选择此解决方案。这不是最差的，但也不是最好的。唯一的原因是它可能更容易理解。
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。
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
身体：
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 变体。
于 2015-07-09T15:49:36.043 回答
11
使用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;
}
如果您没有 std::string_view，请尝试使用 std::experimental::string_view。
于 2017-06-15T08:30:16.420 回答
5
我对DaedalusAlpha 的回答的变化：
它避免了以几次测试为代价来复制参数。
使用 uint8_t 而不是 BYTE。
添加了一些方便的函数来处理字符串，尽管通常输入数据是二进制的并且内部可能有零字节，因此通常不应将其作为字符串进行操作（这通常意味着以空值结尾的数据）。
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）。
文件base64.hpp的一部分：
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base64.cpp：
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);
}
于 2016-02-11T00:03:21.550 回答
3
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;
};
//---------------------------------------------------------------------------
于 2019-12-24T06:40:43.570 回答
2
我用这个：
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;
}
用于vec.bytes访问转换后的数据。
于 2019-12-07T16:05:42.167 回答
1
我首先制作了自己的版本，然后找到了这个主题。
为什么我的版本看起来比这里介绍的其他版本更简单？难道我做错了什么？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;
}
PS：我的方法效果很好。我用Node.js测试了它：
let data = 'stackabuse.com';
let buff = new Buffer(data);
let base64data = buff.toString('base64');
于 2020-03-07T01:20:22.317 回答
0
我喜欢GitHub 上的这个解决方案。
它是一个单独的 hpp 文件，它使用 vector<byte> 类型的原始数据，这与接受的答案不同。
#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;
}
}
于 2021-01-07T12:20:19.020 回答
0
这是我写的一篇文章，它使用联合和位域来实现最大的效率和可读性。
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;
}
于 2021-02-24T15:08:35.357 回答