C + + 将字符串转换为十六进制，反之亦然

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); }

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;
}

为了检查输出，密码本返回: 6e

一个在线 十六进制转换工具也能产生6e，所以它是有效的。

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();
}

类似“ Hello World”的字符串转换为十六进制格式: 48656C6C6F20576F726C64。

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 char 有8位，所以它不是非常可移植的，但是你可以从这里开始。)

你可以试试这个，很有效。

#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;
}

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;
}

这个稍微快一点:

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];
}
}

使用查找表之类的方法是可行的，但是有点过头了，这里有一些非常简单的方法可以把字符串变成十六进制，把十六进制变回字符串:

#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;
}

这将把“ Hello World”转换为“48656c6c6f20576f726c64”，并将这个十六进制值存储在 str1中，还将把“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);
}

这将把 Hello World 转换为48656c6c6f20576f726c64和 打印 it。

#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;
}

我认为有一个更简单、更优雅的解决方案。在某些情况下，上面提到的一些方法甚至可能抛出未处理的异常。这里有一个简单易用的代码(比如从不出错)和非常快的代码。试试看，比较一下速度和紧凑度的结果:

#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';
}

结果就是:

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

在 C + + 17中还有 From _ chars。下面的函数接受一个十六进制字符串并返回一个 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;
}

这里是另一个解决方案，很大程度上受到@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();
}

长度是预期用法中所需的参数。

#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