Question

today I tried to convert a hex string to an unsigned char[]

string test = "fe5f0c";
unsigned char* uchar= (unsigned char *)test.c_str();
cout << uchar << endl;

This resulted in the output of

fe5f0c

hrmpf :-(. The desired behaviour would be as follows:

unsigned char caTest[2]; 
caTest[0] = (unsigned char)0xfe;
caTest[1] = (unsigned char)0x5f;
caTest[2] = (unsigned char)0x0c;
cout << caTest << endl;

which prints unreadable ascii code. As so often I am doing something wrong ^^. Would appreciate any suggestions.

Thanks in advance

Answer 1

Sure, you just have to isolate the bits you are interested in after parsing:

#include <string>
#include <cstdlib>
#include <iostream>

typedef unsigned char byte;

int main()
{
    std::string test = "40414243";
    unsigned long x = strtoul(test.c_str(), 0, 16);
    byte a[] = {byte(x >> 24), byte(x >> 16), byte(x >> 8), byte(x), 0};
    std::cout << a << std::endl;
}

Note that I changed the input string to an eight digit number, since otherwise the array would start with the value 0, and operator<< would interpret that as the end and you wouldn’t be able to see anything.