Dump hex of a buffer, that the format is (almost) identical to the output of `xxd` in Linux, so the dumped text could be parsed by `xxd -r`

dumphex.hpp

#ifndef __DUMP_HEX_HEADER__
#define __DUMP_HEX_HEADER__
#define DH_NUM_BYTES_PER_LINE  16
#define DH_HEX_POS	46	
#define DH_HEX_OFFSET  6
#define DH_HEX_COLUMN_SIZE				8

#define DH_SEPERATOR		' '
#define DH_UNPRINTABLE	'.'

#include <iomanip>
#include <assert.h>
#include <sstream>

//
// Compatile to `xxd -r` in Linux
// Output example:
//
// Dump hex value, size 82
// 000000: 6861 6F72 6568 7572 616F 756C 6123 1199   haorehuraoula#..
// 000010: E2BB BE75 6C72 6162 6575 6C72 6861 6C72   ...ulrabeulrhalr
// 000020: 6575 6368 616C 7265 7568 6C72 6168 6575   euchalreuhlraheu
// 000030: 6C72 6168 656C 7568 616C 6F65 7562 6172   lraheluhaloeubar
// 000040: 6378 6261 6C72 656F 626B 726C 6361 6F6B   cxbalreobkrlcaok
// 000050: 3132                                      12

static std::string dumpToHexString(const unsigned char* ptr, size_t len)
{
	if (ptr == NULL || len == 0)
	{
		return "NULL";
	}
	std::ostringstream overallOss, oss2;
	overallOss << "Dump hex value, size " << len << std::endl;
	overallOss << std::hex << std::uppercase << std::setw(6) << std::setfill('0') << int(0) << ": ";

	size_t offset = 0, pos = 0;
	for (size_t idx = 0; idx < len; idx++)
	{
		offset = idx % DH_NUM_BYTES_PER_LINE;
		if (offset == 0) pos = DH_HEX_OFFSET;

		const unsigned char& byte = ptr[idx];
		overallOss << std::setw(2) << std::setfill('0') << (unsigned) byte;
		pos += 2;

		std::isprint(byte) != 0 ? oss2 << byte : oss2 << DH_UNPRINTABLE;
		if (idx + 1 == len || offset + 1 == DH_NUM_BYTES_PER_LINE)
		{
			overallOss << std::setw(DH_HEX_POS - pos + 2 )
				<< std::setfill(DH_SEPERATOR) << "  " << oss2.str();
			oss2.str("");
			if (idx + 1 != len){
				overallOss << "\n";
				overallOss << std::hex << std::uppercase << std::setw(6) << std::setfill('0') << idx + 1 << ": ";
			}
		}
		else if (offset + 1 == DH_HEX_COLUMN_SIZE)
		{
			overallOss << std::setw(1) << std::setfill(DH_SEPERATOR) << "";
			pos += 1;
		}
		else if (offset % 2 == 1)
		{
			overallOss << std::setw(1) << std::setfill(DH_SEPERATOR) << "";
			pos += 1;
		}
	}
	return overallOss.str();
}

#endif