I searched char* to hex string before but implementation I found adds some non-existent garbage at the end of hex string. I receive packets from socket, and I need to convert them to hex strings for log (null-terminated buffer). Can somebody advise me a good implementation for C++?
Thanks!
Supposing data is a char*. Working example using std::hex:
for(int i=0; i<data_length; ++i)
std::cout << std::hex << (int)data[i];
Or if you want to keep it all in a string:
std::stringstream ss;
for(int i=0; i<data_length; ++i)
ss << std::hex << (int)data[i];
std::string mystr = ss.str();
char* array element directly to int or unsigned int will result in bytes over 0x7F being improperly "sign-extended". You need to first cast the char to uint8_t, then cast that to unsigned int, in order to correctly represent bytes. See this example: stackoverflow.com/questions/62934400Here is something:
char const hex_chars[16] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
string result = "";
for( int i = 0; i < data_length; ++i )
{
char const byte = data[i];
result += hex_chars[ ( byte & 0xF0 ) >> 4 ];
result += hex_chars[ ( byte & 0x0F ) >> 0 ];
}
8 == 4*2 and maximum number in hex is F==15 which requires 4 bits in binary representation, you need two digits in hex to represent a byte. What code does is, it bitmasks (logical AND) each byte first with 1111 0000 then 0000 1111 to only get the part of binary number that fits in a single hex digit; Then if it is the first 4 digit (first hex digit in a two digits pair) of the binary number, we shift it right to use it as 0 to 15, and then we use it as hex_chars index. Hope I helpedThe simplest:
int main()
{
const char* str = "hello";
for (const char* p = str; *p; ++p)
{
printf("%02x", *p);
}
printf("\n");
return 0;
}
I've found good example here Display-char-as-Hexadecimal-String-in-C++:
std::vector<char> randomBytes(n);
file.read(&randomBytes[0], n);
// Displaying bytes: method 1
// --------------------------
for (auto& el : randomBytes)
std::cout << std::setfill('0') << std::setw(2) << std::hex << (0xff & (unsigned int)el);
std::cout << '\n';
// Displaying bytes: method 2
// --------------------------
for (auto& el : randomBytes)
printf("%02hhx", el);
std::cout << '\n';
return 0;
Method 1 as shown above is probably the more C++ way:
Cast to an unsigned int
Usestd::hexto represent the value as hexadecimal digits
Usestd::setwandstd::setfillfrom<iomanip>to format
Note that you need to mask the cast int against0xffto display the least significant byte:
(0xff & (unsigned int)el).Otherwise, if the highest bit is set the cast will result in the three most significant bytes being set to
ff.
std::vector<unsigned char> (which is probably a bit better for random byte arrays), then you don't need the 0xff & part.Code snippet above provides incorrect byte order in string, so I fixed it a bit.
char const hex[16] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B','C','D','E','F'};
std::string byte_2_str(char* bytes, int size) {
std::string str;
for (int i = 0; i < size; ++i) {
const char ch = bytes[i];
str.append(&hex[(ch & 0xF0) >> 4], 1);
str.append(&hex[ch & 0xF], 1);
}
return str;
}
Using boost:
#include <boost/algorithm/hex.hpp>
std::string s("tralalalala");
std::string result;
result.reserve(s.size() * 2);
boost::algorithm::hex_lower(s, std::back_inserter(result));
You can try this code for converting bytes from packet to a null-terminated string and store to "string" variable for processing.
const int buffer_size = 2048;
// variable for storing buffer as printable HEX string
char data[buffer_size*2];
// receive message from socket
int ret = recvfrom(sock, buffer, sizeofbuffer, 0, reinterpret_cast<SOCKADDR *>(&from), &size);
// bytes converting cycle
for (int i=0,j=0; i<ret; i++,j+=2){
char res[2];
itoa((buffer[i] & 0xFF), res, 16);
if (res[1] == 0) {
data[j] = 0x30; data[j+1] = res[0];
}else {
data[j] = res[0]; data[j + 1] = res[1];
}
}
// Null-Terminating the string with converted buffer
data[(ret * 2)] = 0;
When we send message with hex bytes 0x01020E0F, variable "data" had char array with string "01020e0f".
