convert string to hex array c++

Question

I have a string like

string test = "48656c6c6f20576f726c64";

and I would like to convert it to

unsigned char state[] = {0x00, 0x11, 0x22, 0x33, 0x44, 0x55, 0x66, 0x77, 
                           0x88, 0x99, 0xaa, 0xbb, 0xcc, 0xdd, 0xee, 0xff};

unsigned char bytearray[60];
int w;
for (w=0;w<str.length();w+2) {
    bytearray[w] = "0x" + str2[w];  
}

It doesn't seem to work. Any help would be appreciated

You need the [`std::hex`](https://en.cppreference.com/w/cpp/io/manip/hex)` iostream manipulator, and a `std::ostringstream.` or a `std::istringstream` — πάντα ῥεῖ, Jul 21 '18 at 13:53
Firstly, you are conceptually assigning multiple characters, "0x" (2 characters), to a single character element, `bytearray[w]`. I recommend reviewing the sections about data types in your favorite C++ reference. A single element in a character array can only contain a single character, not multiple characters. — Thomas Matthews, Jul 21 '18 at 16:33

score 0 · Answer 1 · answered Jul 21 '18 at 18:28

Try something more like this instead:

#include <vector>
#include <string>

std::string test = "48656c6c6f20576f726c64"; 
size_t numbytes = test.size() / 2;

std::vector<unsigned char> bytearray;
bytearray.reserve(numbytes);

for (size_t w = 0, x = 0; w < numbytes; ++w, x += 2) {
    unsigned char b;

    char c = test[x];
    if ((c >= '0') && (c <= '9'))
        b = (c - '0');
    else if ((c >= 'A') && (c <= 'F'))
        b = 10 + (c - 'A');
    else if ((c >= 'a') && (c <= 'f'))
        b = 10 + (c - 'a');
    else {
        // error!
        break;
    }

    b <<= 4;

    c = test[x+1];
    if ((c >= '0') && (c <= '9'))
        b |= (c - '0');
    else if ((c >= 'A') && (c <= 'F'))
        b |= 10 + (c - 'A');
    else if ((c >= 'a') && (c <= 'f'))
        b |= 10 + (c - 'a');
    else {
        // error!
        break;
    }

    bytearray.push_back(b);
}

// use bytearray as needed...

Alternatively:

#include <vector>
#include <string>
#include <iomanip>

std::string test = "48656c6c6f20576f726c64"; 
size_t numbytes = test.size() / 2;

std::vector<unsigned char> bytearray;
bytearray.reserve(numbytes);

for(size_t w = 0, x = 0; w < numbytes; ++w, x += 2)
{
    std::istringstream iss(test.substr(x, 2));
    unsigned short b;

    if (!(iss >> std::hex >> b)) {
        // error!
        break;
    }

    bytearray.push_back(static_cast<unsigned char>(b));
}

// use bytearray as needed...

Live Demo

score -1 · Answer 2 · answered Jul 21 '18 at 15:28

-1

explained here C++ convert hex string to signed integer

so do something like this:

unsigned int x;  
std::string substring; // you will need to figure out how to get this
std::stringstream ss;
ss << std::hex << substring;
ss >> x;

x is what you would need to store an your array. "48" would actually be a parsed part of your string. Look here So you might need to change the type. Play around with it. Also i think you were parsing your string incorrectly. check this out Split string using loop to specific length sub-units

answered Jul 21 '18 at 15:28

phaile

13
2

sorry i miss typed. i meant to say substing would actually be the parsed part of your string. your array is a char array so you might need to change the type of x. Also i think you were parsing your string incorrectly. check this out Split string using loop to specific length sub-units – phaile Jul 21 '18 at 15:31
hey phaile thank you for the reply. I already used your above method and fed it to string test but I want to make it in 0x00, 0x11 format and put it into the char array – Ismail Issa Jul 21 '18 at 16:09

convert string to hex array c++

2 Answers2