Convert a vector<char> to a string with a conversion

Question

I'd like to convert a vector<char> to a std::string and do a conversion one the way.

I'm almost there, but the result of the code below is a vector<string>, while I'd like to have one string (a concatenation of all the string parts in the vector).

See my code example for details.

string ConvertHexToAscii(const char input)
{
    std::ostringstream oss;
    oss << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(input);
    return oss.str();
}

vector<char> readBuffer; // this is my input

readBuffer.push_back(0x1c);
readBuffer.push_back(0x09);

vector<string> resultVec;

std::transform(readBuffer.begin(), readBuffer.end()
    , back_inserter(resultVec)
    , ConvertHexToAscii);

// resultVec[0] = "1C";
// resultVec[1] = "09";

The result I need is a string containing "1C09". How to achieve that with std::transform?

Answer 1

You were almost there; this works:

std::stringstream sstr;
std::transform(
    input.begin(), input.end(),
    std::ostream_iterator<std::string>(sstr, ""),
    ConvertHexToAscii);

But unfortunately this instantiates quite a lot of string streams, which is inefficient. Ideally, the ConvertHexToAscii (misnamed, by the way! C++ doesn’t know about encodings) function would directly use the underlying stream.

Answer 2

#include <iostream>
#include <vector>
#include <iomanip>
#include <sstream>
#include <numeric>

std::string ConvertHexToAscii(std::string acc, char input)
{
  std::ostringstream oss;
  oss << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(input);
  return acc + oss.str();
}


int main() {
  std::vector<char> readBuffer; // this is my input
  readBuffer.push_back(0x1c);
  readBuffer.push_back(0x09);

  std::cout << std::accumulate(readBuffer.begin(), readBuffer.end()
          , std::string(), ConvertHexToAscii) << std::endl;

  return 0;
}

Answer 3

create your own back_insert_iterator (look at the code in your stl lib, it's fairly simple) for string types of which operator = is defined as

template< class string_type, class value_type >
class back_insert_iterator
{
public:
  back_insert_iterator< _string_type >& operator = ( const value_type& val )
  {
    container->append( val )
    return *this;
  }
};