C++ 将字符串转换为十六进制，反之亦然

Question

在 C++ 中将字符串转换为十六进制的最佳方法是什么，反之亦然？

例子：

• 像"Hello World"这样的十六进制格式的字符串： 48656C6C6F20576F726C64
• 从十六进制48656C6C6F20576F726C64到字符串： "Hello World"

Answer 1

像“Hello World”这样的字符串到十六进制格式：48656C6C6F20576F726C64。

啊，给你：

#include <string>

std::string string_to_hex(const std::string& input)
{
    static const char hex_digits[] = "0123456789ABCDEF";

    std::string output;
    output.reserve(input.length() * 2);
    for (unsigned char c : input)
    {
        output.push_back(hex_digits[c >> 4]);
        output.push_back(hex_digits[c & 15]);
    }
    return output;
}

#include <stdexcept>

int hex_value(unsigned char hex_digit)
{
    static const signed char hex_values[256] = {
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
         0,  1,  2,  3,  4,  5,  6,  7,  8,  9, -1, -1, -1, -1, -1, -1,
        -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    };
    int value = hex_values[hex_digit];
    if (value == -1) throw std::invalid_argument("invalid hex digit");
    return value;
}

std::string hex_to_string(const std::string& input)
{
    const auto len = input.length();
    if (len & 1) throw std::invalid_argument("odd length");

    std::string output;
    output.reserve(len / 2);
    for (auto it = input.begin(); it != input.end(); )
    {
        int hi = hex_value(*it++);
        int lo = hex_value(*it++);
        output.push_back(hi << 4 | lo);
    }
    return output;
}

（这里假设一个字符有 8 位，所以它不是很便携，但你可以从这里获取它。）

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

使用查找表等工作，但只是矫枉过正，这里有一些非常简单的方法将字符串转换为十六进制并将十六进制返回到字符串：

#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 4

我认为有一个更简单、更优雅的解决方案。 在某些情况下，上述一些方法甚至可能抛出未处理的异常。 这是一个万无一失（永远不会出错）和非常快速的代码。 只需尝试一下并比较速度和紧凑性方面的结果：

#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;
    }
}

测试代码：

#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';
}

结果是：

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

Answer 5

你可以试试这个。 它正在工作...

#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 6

从 C++17 开始，还有std::from_chars 。 以下函数接受一串十六进制字符并返回 T 的向量：

#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 (std::size_t 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 7

使用标准库的最简单示例。

#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;
}

要检查输出，键盘返回：6e

并且在线ascii 到十六进制转换工具也可以生成 6e。 所以它有效。

你也可以这样做：

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 8

这有点快：

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 9

这会将 Hello World 转换为 48656c6c6f20576f726c64 并打印出来。

#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;
}

Answer 10

这是另一个解决方案，主要受@fredoverflow 的启发。

/**
 * 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();
}

长度是预期用途中的必需参数。

Answer 11

这会将“Hello World”转换为“48656c6c6f20576f726c64”，并将此十六进制值存储在 str1 中，还将“48656c6c6f20576f726c64”转换为“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 12

#include "boost/algorithm/hex.hpp"
std::string hexed = boost::algorithm::hex(std::string("input"));

https://www.boost.org/doc/libs/1_78_0/boost/algorithm/hex.hpp

Answer 13

这适用于打印 UTF-8 编码的字符串（长度可变）

// std::string
void printHex1(const std::string & str)
{
  printf("%s 1: ", str.c_str());
  for (size_t i = 0; i < str.size(); i++)
    printf("%X ", str[i]);
  printf("\n");
}

// c-style string
void printHex2(const char * buf)
{
  printf("%s 2: ", buf);
  size_t i = 0;
  while (buf[i] != 0) {
    printf("%X ", buf[i]);
    i++;
  }
  printf("\n");
}

小测试

std::string test_vector = "Cigueña";
char c_vector[128];
strncpy(c_vector, test_vector.c_str(), 128);
printHex1(test_vector);
printHex2(c_vector);

输出：

Cigueña 1: 43 69 67 75 65 FFFFFFC3 FFFFFFB1 61 
Cigueña 2: 43 69 67 75 65 FFFFFFC3 FFFFFFB1 61 

查看UTF-8字符如何使用更多ñ进行编码。

Answer 14

为什么没有人使用 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;
}