c++ - 将 unsigned char * 转换为 hexstring

Question

下面的代码采用一个十六进制字符串(每个字节都表示为其对应的十六进制值)将其转换为 unsigned char * 缓冲区，然后再转换回十六进制字符串。此代码正在测试从 unsigned char* 缓冲区到十六进制字符串的转换我需要通过网络将其发送到接收进程。我选择了十六进制字符串，因为 unsigned char 可以在 0 到 255 的范围内，并且 127 之后没有可打印字符。下面的代码只是告诉了让我烦恼的部分。它在评论中。

#include <iostream>
#include <sstream>
#include <iomanip>

using namespace std;
// converts a hexstring to corresponding integer. i.e "c0" - > 192
int convertHexStringToInt(const string & hexString)
{
  stringstream geek;
  int x=0;

  geek << std::hex << hexString;
  geek >> x;

  return x;
}

// converts a complete hexstring to unsigned char * buffer
void convertHexStringToUnsignedCharBuffer(string hexString, unsigned char* 
hexBuffer)
{
  int i=0;
  while(hexString.length())
  {
    string hexStringPart = hexString.substr(0,2);
    hexString = hexString.substr(2);
    int hexStringOneByte = convertHexStringToInt (hexStringPart);
    hexBuffer[i] = static_cast<unsigned char>((hexStringOneByte & 0xFF)) ;
    i++;
  }
}

int main()
{
  //below hex string is a hex representation of a unsigned char * buffer.
  //this is generated by an excryption algorithm in unsigned char* format
  //I am converting it to hex string to make it printable for verification pupose.
  //and takes the hexstring as inpuit here to test the conversion logic.
  string inputHexString = "552027e33844dd7b71676b963c0b8e20";
  string outputHexString;
  stringstream geek;

  unsigned char * hexBuffer = new unsigned char[inputHexString.length()/2];
  convertHexStringToUnsignedCharBuffer(inputHexString, hexBuffer);

  for (int i=0;i<inputHexString.length()/2;i++)
  {
    geek <<std::hex << std::setw(2) << std::setfill('0')<<(0xFF&hexBuffer[i]); // this works
    //geek <<std::hex << std::setw(2) << std::setfill('0')<<(hexBuffer[i]); -- > this does not work
    // I am not able to figure out why I need to do the bit wise and operation with unsigned char "0xFF&hexBuffer[i]"
    // without this the conversion does not work for individual bytes having ascii values more than 127.
  }

  geek >> outputHexString;

  cout << "input hex string:  " << inputHexString<<endl;
  cout << "output hex string: " << outputHexString<<endl;
  if(0 == inputHexString.compare(outputHexString))
    cout<<"hex encoding successful"<<endl;
  else
    cout<<"hex encoding failed"<<endl;

  if(NULL != hexBuffer)
      delete[] hexBuffer;

  return 0;
}

// output
// can some one explain ? I am sure its something silly that I am missing.

Answer 1

C++20 方式:

unsigned char* data = new unsigned char[]{ "Hello world\n\t\r\0" };
std::size_t data_size = sizeof("Hello world\n\t\r\0") - 1;

auto sp = std::span(data, data_size );
std::transform( sp.begin(), sp.end(),
                std::ostream_iterator<std::string>(std::cout),
                [](unsigned char c) -> std::string {
                    return std::format("{:02X}", int(c));
                });

或者如果你想将结果存储到字符串中:

std::string result{};
result.reserve(size * 2 + 1);
std::transform( sp.begin(), sp.end(),
                std::back_inserter(result),
                [](unsigned char c) -> std::string {
                    return std::format("{:02X}", int(c));
                });

Output:
48656C6C6F20776F726C640A090D00