问题描述

我尝试使用 boost base64 编码器，我找到了一个示例，但我得到了异常

I trying to use boost base64 encoder, I found an example but I got and exception

typedef 
transform_width< binary_from_base64<std::string::const_iterator>, 8, 6 > it_binary_t

我用过的

std::string b64E(it_binary_t(Encrip.begin()), it_binary_t(Encrip.end()));

我明白了

agentid_coder.exe 中 0x75b1b9bc 处未处理的异常:Microsoft C++异常:内存中的 boost::archive::iterators::dataflow_exception位置 0x0046ed94..

Unhandled exception at 0x75b1b9bc in agentid_coder.exe: Microsoft C++ exception: boost::archive::iterators::dataflow_exception at memory location 0x0046ed94..

我找到了这个解决方法，但我得到了相同的结果

I found this workaround but I get the same result

 string dec( 
        it_binary_t(Encrip.begin()), 
        it_binary_t(Encrip.begin() + Encrip.length() - 1) 
        ); 

我正在使用 MSVS2008 和 boost 1.38

I am using MSVS2008 and boost 1.38

推荐答案

很遗憾 iterator_adaptors binary_from_base64 和 transform_width 这两个组合不是一个完整的 base64 编码器/解码器.Base64 将 24 位(3 个字节)的组表示为 4 个字符，每个字符编码 6 位.如果输入数据不是这样的 3 字节组的整数倍，则必须用一或两个零字节填充.为了指示添加了多少填充字节，将一或两个 = 字符附加到编码字符串.

Unfortunately the combination of the two iterator_adaptors binary_from_base64 and transform_width is not a complete base64 encoder/decoder. Base64 represents groups of 24 bits (3 bytes) as 4 characters, each of which encodes 6 bits. If the input data is not an integer multiple of such 3 byte groups it has to be padded with one or two zero bytes. To indicate how many padding bytes were added, one or two = characters are appended to the encoded string.

transform_width，负责 8 位二进制到 6 位整数的转换不会自动应用此填充，它确实由用户完成.一个简单的例子:

transform_width, which is responsible for the 8bit binary to 6bit integer conversion does not apply this padding automatically, it has do be done by the user. A simple example:

#include <boost/archive/iterators/base64_from_binary.hpp>
#include <boost/archive/iterators/binary_from_base64.hpp>
#include <boost/archive/iterators/transform_width.hpp>
#include <boost/archive/iterators/insert_linebreaks.hpp>
#include <boost/archive/iterators/remove_whitespace.hpp>
#include <iostream>
#include <string>

using namespace boost::archive::iterators;
using namespace std;

int main(int argc, char **argv) {
  typedef transform_width< binary_from_base64<remove_whitespace<string::const_iterator> >, 8, 6 > it_binary_t;
  typedef insert_linebreaks<base64_from_binary<transform_width<string::const_iterator,6,8> >, 72 > it_base64_t;
  string s;
  getline(cin, s, '
');
  cout << "Your string is: '"<<s<<"'"<<endl;

  // Encode
  unsigned int writePaddChars = (3-s.length()%3)%3;
  string base64(it_base64_t(s.begin()),it_base64_t(s.end()));
  base64.append(writePaddChars,'=');

  cout << "Base64 representation: " << base64 << endl;

  // Decode
  unsigned int paddChars = count(base64.begin(), base64.end(), '=');
  std::replace(base64.begin(),base64.end(),'=','A'); // replace '=' by base64 encoding of ''
  string result(it_binary_t(base64.begin()), it_binary_t(base64.end())); // decode
  result.erase(result.end()-paddChars,result.end());  // erase padding '' characters
  cout << "Decoded: " << result << endl;
  return 0;
}

请注意，我添加了 insert_linebreaks 和 remove_whitespace 迭代器，因此 base64 输出的格式很好，并且可以解码带有换行符的 base64 输入.不过这些都是可选的.

Note that I added the insert_linebreaks and remove_whitespace iterators, so that the base64 output is nicely formatted and base64 input with line breaks can be decoded. These are optional though.

使用需要不同填充的不同输入字符串运行:

Run with different input strings which require different padding:

$ ./base64example
Hello World!
Your string is: 'Hello World!'
Base64 representation: SGVsbG8gV29ybGQh
Decoded: Hello World!
$ ./base64example
Hello World!!
Your string is: 'Hello World!!'
Base64 representation: SGVsbG8gV29ybGQhIQ==
Decoded: Hello World!!
$ ./base64example
Hello World!!!
Your string is: 'Hello World!!!'
Base64 representation: SGVsbG8gV29ybGQhISE=
Decoded: Hello World!!!

您可以使用此 online-encoder/decoder 检查 base64 字符串.

You can check the base64 strings with this online-encoder/decoder.

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