How to convert Byte Array to Hexadecimal String in C++? - c++

Question

I am looking for a fastest way to convert a byte array of arbitrary length to a hexadecimal string. This question has been fully answered here at StackOverflow for C#. Some solutions in C++ can be found here.
Are there any "turnkey" or "ready-made" solutions to a problem? C-style solutions are welcome.

Answer 1

#include <vector>
#include <iostream>
#include <algorithm>
#include <string>
#include <iterator>
#include <sstream>
#include <iomanip>
int main()
{
std::vector<unsigned char> v;
v.push_back( 1 );
v.push_back( 2 );
v.push_back( 3 );
v.push_back( 4 );
std::ostringstream ss;
ss << std::hex << std::uppercase << std::setfill( '0' );
std::for_each( v.cbegin(), v.cend(), [&]( int c ) { ss << std::setw( 2 ) << c; } );
std::string result = ss.str();
std::cout << result << std::endl;
return 0;
}
Or, if you've got a compiler that supports uniform initialization syntax and range based for loops you can save a few lines.
#include <vector>
#include <sstream>
#include <string>
#include <iostream>
#include <iomanip>
int main()
{
std::vector<unsigned char> v { 1, 2, 3, 4 };
std::ostringstream ss;
ss << std::hex << std::uppercase << std::setfill( '0' );
for( int c : v ) {
ss << std::setw( 2 ) << c;
}
std::string result = ss.str();
std::cout << result << std::endl;
}

Answer 2

Use boost::alogorithm::hex
std::vector<unsigned char> v;
v.push_back(1);
v.push_back(2);
v.push_back(3);
v.push_back(4);
std::string res;
boost::algorithm::hex(v.begin(), v.end(), back_inserter(res));

Answer 3

You can use the C++ Standard Library and or you can use boost::lexical_cast
#include <iostream>
#include <string>
#include <array>
#include <vector>
#include <sstream>
#include <iomanip>
#include <algorithm>
using namespace std;
// use this macro for c++11 feature
#define USE_CPP11
int main(int argc, char* argv[])
{
array<unsigned char, 3> hexArr = {0x01, 0xff, 0x55};
const char separator = ' '; // separator between two numbers
ostringstream os;
os << hex << setfill('0'); // set the stream to hex with 0 fill
#ifdef USE_CPP11
std::for_each(std::begin(hexArr), std::end(hexArr), [&os, &separator] (int i)
{
os << setw(2) << i << separator;
});
#else // c++03
typedef array<unsigned char, 3>::const_iterator const_iterator;
for (const_iterator it = hexArr.begin(); it != hexArr.end(); ++it)
{
os << setw(2) << int(*it) << separator;
}
#endif
os << dec << setfill(' '); // reset the stream to "original"
// print the string
cout << "the string array is: " << os.str() << endl;
return EXIT_SUCCESS;
}

Answer 4

One of the fastest way I know in C++ 11:
template <size_t byteCount>
string BytesArrayToHexString( const std::array<byte, byteCount>& src )
{
static const char table[] = "0123456789ABCDEF";
std::array<char, 2 * byteCount + 1> dst;
const byte* srcPtr = &src[0];
char* dstPtr = &dst[0];
for (auto count = byteCount; count > 0; --count)
{
unsigned char c = *srcPtr++;
*dstPtr++ = table[c >> 4];
*dstPtr++ = table[c & 0x0f];
}
*dstPtr = 0;
return &dst[0];
}
A good compiler should not have any problem to apply SSE optimization on this....