C ++ convert string to hexadecimal and vice versa

Question

What is the best way to convert a string to hex and vice versa in C ++?

Example:

• String type "Hello World" in hexadecimal format: 48656C6C6F20576F726C64
• And from hex 48656C6C6F20576F726C64 to the line: "Hello World"

Answer 1

String type "Hello World" in hexadecimal format: 48656C6C6F20576F726C64.

Ah, here you are:

 #include <string> std::string string_to_hex(const std::string& input) { static const char* const lut = "0123456789ABCDEF"; size_t len = input.length(); std::string output; output.reserve(2 * len); for (size_t i = 0; i < len; ++i) { const unsigned char c = input[i]; output.push_back(lut[c >> 4]); output.push_back(lut[c & 15]); } return output; } #include <algorithm> #include <stdexcept> std::string hex_to_string(const std::string& input) { static const char* const lut = "0123456789ABCDEF"; size_t len = input.length(); if (len & 1) throw std::invalid_argument("odd length"); std::string output; output.reserve(len / 2); for (size_t i = 0; i < len; i += 2) { char a = input[i]; const char* p = std::lower_bound(lut, lut + 16, a); if (*p != a) throw std::invalid_argument("not a hex digit"); char b = input[i + 1]; const char* q = std::lower_bound(lut, lut + 16, b); if (*q != b) throw std::invalid_argument("not a hex digit"); output.push_back(((p - lut) << 4) | (q - lut)); } return output; } 

(It is assumed that char has 8 bits, so it is not very portable, but you can take it here.)

Answer 2

 string ToHex(const string& s, bool upper_case /* = true */) { ostringstream ret; for (string::size_type i = 0; i < s.length(); ++i) ret << std::hex << std::setfill('0') << std::setw(2) << (upper_case ? std::uppercase : std::nouppercase) << (int)s[i]; return ret.str(); } int FromHex(const string &s) { return strtoul(s.c_str(), NULL, 16); } 

Answer 3

You can try this. He works...

 #include <algorithm> #include <sstream> #include <iostream> #include <iterator> #include <iomanip> namespace { const std::string test="hello world"; } int main() { std::ostringstream result; result << std::setw(2) << std::setfill('0') << std::hex << std::uppercase; std::copy(test.begin(), test.end(), std::ostream_iterator<unsigned int>(result, " ")); std::cout << test << ":" << result.str() << std::endl; } 

Answer 4

Using lookup tables, etc. works, but just brute force, here are some very simple ways to translate a string into hexadecimal and hexadecimal back into string:

 #include <stdexcept> #include <sstream> #include <iomanip> #include <string> #include <cstdint> std::string string_to_hex(const std::string& in) { std::stringstream ss; ss << std::hex << std::setfill('0'); for (size_t i = 0; in.length() > i; ++i) { ss << std::setw(2) << static_cast<unsigned int>(static_cast<unsigned char>(in[i])); } return ss.str(); } std::string hex_to_string(const std::string& in) { std::string output; if ((in.length() % 2) != 0) { throw std::runtime_error("String is not valid length ..."); } size_t cnt = in.length() / 2; for (size_t i = 0; cnt > i; ++i) { uint32_t s = 0; std::stringstream ss; ss << std::hex << in.substr(i * 2, 2); ss >> s; output.push_back(static_cast<unsigned char>(s)); } return output; } 

Answer 5

The simplest example using the standard library.

 #include <iostream> using namespace std; int main() { char c = 'n'; cout << "HEX " << hex << (int)c << endl; // output in hexadecimal cout << "ASC" << c << endl; // output in ascii return 0; } 

To check the output, codepad returns: 6e

and the ascii-to-hexadecimal online tool also gives 6e. So it works.

You can also do this:

 template<class T> std::string toHexString(const T& value, int width) { std::ostringstream oss; oss << hex; if (width > 0) { oss << setw(width) << setfill('0'); } oss << value; return oss.str(); } 

Answer 6

I think there is a much simpler and more elegant solution. Some of the above methods may even throw unhandled exceptions in some cases. Here is a fool (as never mistaken) and very fast code. Just try and compare the results in terms of speed and compactness:

 #include <string> // Convert string of chars to its representative string of hex numbers void stream2hex(const std::string str, std::string& hexstr, bool capital = false) { hexstr.resize(str.size() * 2); const size_t a = capital ? 'A' - 1 : 'a' - 1; for (size_t i = 0, c = str[0] & 0xFF; i < hexstr.size(); c = str[i / 2] & 0xFF) { hexstr[i++] = c > 0x9F ? (c / 16 - 9) | a : c / 16 | '0'; hexstr[i++] = (c & 0xF) > 9 ? (c % 16 - 9) | a : c % 16 | '0'; } } // Convert string of hex numbers to its equivalent char-stream void hex2stream(const std::string hexstr, std::string& str) { str.resize((hexstr.size() + 1) / 2); for (size_t i = 0, j = 0; i < str.size(); i++, j++) { str[i] = (hexstr[j] & '@' ? hexstr[j] + 9 : hexstr[j]) << 4, j++; str[i] |= (hexstr[j] & '@' ? hexstr[j] + 9 : hexstr[j]) & 0xF; } } 

Test the code :

 #include <iostream> int main() { std::string s = "Hello World!"; std::cout << "original string: " << s << '\n'; stream2hex(s, s); std::cout << "hex format: " << s << '\n'; hex2stream(s, s); std::cout << "original one: " << s << '\n'; } 

and the result:

 original string: Hello World! hex format: 48656C6C6F20576F726C6421 original one: Hello World! 

Answer 7

This is a bit faster:

 static const char* s_hexTable[256] = { "00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "0a", "0b", "0c", "0d", "0e", "0f", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "1a", "1b", "1c", "1d", "1e", "1f", "20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "2a", "2b", "2c", "2d", "2e", "2f", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "3a", "3b", "3c", "3d", "3e", "3f", "40", "41", "42", "43", "44", "45", "46", "47", "48", "49", "4a", "4b", "4c", "4d", "4e", "4f", "50", "51", "52", "53", "54", "55", "56", "57", "58", "59", "5a", "5b", "5c", "5d", "5e", "5f", "60", "61", "62", "63", "64", "65", "66", "67", "68", "69", "6a", "6b", "6c", "6d", "6e", "6f", "70", "71", "72", "73", "74", "75", "76", "77", "78", "79", "7a", "7b", "7c", "7d", "7e", "7f", "80", "81", "82", "83", "84", "85", "86", "87", "88", "89", "8a", "8b", "8c", "8d", "8e", "8f", "90", "91", "92", "93", "94", "95", "96", "97", "98", "99", "9a", "9b", "9c", "9d", "9e", "9f", "a0", "a1", "a2", "a3", "a4", "a5", "a6", "a7", "a8", "a9", "aa", "ab", "ac", "ad", "ae", "af", "b0", "b1", "b2", "b3", "b4", "b5", "b6", "b7", "b8", "b9", "ba", "bb", "bc", "bd", "be", "bf", "c0", "c1", "c2", "c3", "c4", "c5", "c6", "c7", "c8", "c9", "ca", "cb", "cc", "cd", "ce", "cf", "d0", "d1", "d2", "d3", "d4", "d5", "d6", "d7", "d8", "d9", "da", "db", "dc", "dd", "de", "df", "e0", "e1", "e2", "e3", "e4", "e5", "e6", "e7", "e8", "e9", "ea", "eb", "ec", "ed", "ee", "ef", "f0", "f1", "f2", "f3", "f4", "f5", "f6", "f7", "f8", "f9", "fa", "fb", "fc", "fd", "fe", "ff" }; // Convert binary data sequence [beginIt, endIt) to hexadecimal string void dataToHexString(const uint8_t*const beginIt, const uint8_t*const endIt, string& str) { str.clear(); str.reserve((endIt - beginIt) * 2); for(const uint8_t* it(beginIt); it != endIt; ++it) { str += s_hexTable[*it]; } } 

Answer 8

Starting with C ++ 17, there is also std :: from_chars . The following function takes a string of hexadecimal characters and returns a vector T:

 #include <charconv> template<typename T> std::vector<T> hexstr_to_vec(const std::string& str, unsigned char chars_per_num = 2) { std::vector<T> out(str.size() / chars_per_num, 0); T value; for (int i = 0; i < str.size() / chars_per_num; i++) { std::from_chars<T>( str.data() + (i * chars_per_num), str.data() + (i * chars_per_num) + chars_per_num, value, 16 ); out[i] = value; } return out; } 

Answer 9

This converts the "Hello World" to "48656c6c6f20576f726c64" and saves this hexadecimal value to str1, and also converts the "48656c6c6f20576f726c64" to "Hello World".

 #include <iostream> #include<sstream> using namespace std; int hexCharToInt(char); string hexToString(string); int main() { std::string str; std::stringstream str1; str="Hello World"; for(int i=0;i<str.length();i++){ str1 << std::hex << (int)str.at(i); } std::cout << str1.str() <<"\n"; string test = "48656c6c6f20576f726c64"; std::cout << hexToString(test) <<"\n"; return 0; } string hexToString(string str){ std::stringstream HexString; for(int i=0;i<str.length();i++){ char a = str.at(i++); char b = str.at(i); int x = hexCharToInt(a); int y = hexCharToInt(b); HexString << (char)((16*x)+y); } return HexString.str(); } int hexCharToInt(char a){ if(a>='0' && a<='9') return(a-48); else if(a>='A' && a<='Z') return(a-55); else return(a-87); } 

Answer 10

Why has no one used sprintf?

 #include <string> #include <stdio.h> static const std::string str = "hello world!"; int main() { //copy the data from the string to a char array char *strarr = new char[str.size()+1]; strarr[str.size()+1] = 0; //set the null terminator memcpy(strarr, str.c_str(),str.size()); //memory copy to the char array printf(strarr); printf("\n\nHEX: "); //now print the data for(int i = 0; i < str.size()+1; i++) { char x = strarr[i]; sprintf("%x ", reinterpret_cast<const char*>(x)); } //DO NOT FORGET TO DELETE delete(strarr); return 0; } 

Answer 11

Here's another solution, heavily inspired by @fredoverflow's solution.

 /** * Return hexadecimal representation of the input binary sequence */ std::string hexitize(const std::vector<char>& input, const char* const digits = "0123456789ABCDEF") { std::ostringstream output; for (unsigned char gap = 0, beg = input[gap]; gap < input.length(); beg = input[++gap]) output << digits[beg >> 4] << digits[beg & 15]; return output.str(); } 

Length was a must in the intended

Answer 12

This will convert Hello World to 48656c6c6f20576f726c64 and print .

 #include <iostream> #include <cstring> using namespace std; int main() { char hello[20]="Hello World"; for(unsigned int i=0; i<strlen(hello); i++) cout << hex << (int) hello[i]; return 0; }