CODEWITHSUNDEEP
c++stringhexbyte
xSarah
xSarah

Reputation: 3

C++ how to convert string characters to exact hex bytes

To start off: I have an app that takes a byte array and loads assembly from it.

My idea, to prevent (easy)piracy, was to have an encrypted string on server, download it on client, decrypt it to get for example: std::string decrypted = "0x4D, 0x5A, 0x90, 0x0, 0x3, 0x0, 0x0, 0x0, 0x4";

Then to convert from string to binary(byte array) so it would be

uint8_t binary[] = { 0x4D, 0x5A, 0x90, 0x0, 0x3, 0x0, 0x0, 0x0, 0x4 };

And then continue as it was before, but after lots of googling I couldn't find much info on such direct conversion between regular string and byte array. Thank you for any help! -Sarah

Upvotes: 0

Views: 995

Answers (3)

Yun
Yun

Reputation: 3812

Use std::stoul to interpret a string as an unsigned integer. The unsigned integer can then be cast to a uint8_t type.

One method of parsing the entire string is by using a stringstream.

Code example:

#include <cstdint>
#include <iostream>
#include <sstream>
#include <string>
#include <vector>

int main()
{
    // Input string and output vector
    std::string const decrypted{"0x4D, 0x5A, 0x90, 0x0, 0x3, 0x0, 0x0, 0x0, 0x4"};
    std::vector<std::uint8_t> bytes;

    // Parse the string and fill the output vector
    std::istringstream decryptedStringStream{decrypted};
    std::string decryptedElement;
    while (getline(decryptedStringStream, decryptedElement, ','))
    {
        auto const byte = static_cast<std::uint8_t>(std::stoul(decryptedElement, nullptr, 16));
        bytes.push_back(byte);
    }

    // Print the results (in base 10)
    for (auto const &e : bytes)                                                                             
        std::cout << static_cast<int>(e) << '\n';
}

Upvotes: 1

blastpolak
blastpolak

Reputation: 151

First of all, you should get rid of ", ". Then you can parse char by char, doing bitwise leftshift on every second char and saving as byte

char firstchar = HexCharToByte('5');
char secondchar = HexCharToByte('D');
char result = firstchar | (secondchar << 4);
printf("%%hhu", result); //93

Where HexCharToByte is (upper chars only):

char HexCharToByte(char ch) => ch > 57 ? (ch - 55) : (ch - 48);

This is fast enough method of parsing hex chars.

Upvotes: 0

Some programmer dude
Some programmer dude

Reputation: 409136

You could use std::stoi in a loop.

It gives you the ending position of the number, which you can then use to check if the string is at its end, or if it's a comma. If it's a comma skip it. Then call std::stoi again using the position as the string to parse.

It's not the most effective, but should work fine.

Upvotes: 2

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