CString Hex value conversion to Byte Array

Question

I have been trying to carry out a conversion from CString that contains Hex string to a Byte array and have been

unsuccessful so far. I have looked on forums and none of them seem to help so far. Is there a function with just a few

lines of code to do this conversion?

My code:

BYTE abyData[8];    // BYTE = unsigned char

CString sByte = "0E00000000000400";

Expecting:

abyData[0] = 0x0E;
abyData[6] = 0x04; // etc.

your example actually shows each unsigned char containing a string, which isn't right ... — Useless
– Useless, Commented Sep 19, 2012 at 11:39

Kerrek SB · Accepted Answer · 2012-09-19 11:35:54Z

3

You can simply gobble up two characters at a time:

unsigned int value(char c)
{
    if (c >= '0' && c <= '9') { return c - '0'; }
    if (c >= 'A' && c <= 'F') { return c - 'A' + 10; }
    if (c >= 'a' && c <= 'f') { return c - 'a' + 10; }

    return -1; // Error!
}

for (unsigned int i = 0; i != 8; ++i)
{
    abyData[i] = value(sByte[2 * i]) * 16 + value(sByte[2 * i + 1]);
}

Of course 8 should be the size of your array, and you should ensure that the string is precisely twice as long. A checking version of this would make sure that each character is a valid hex digit and signal some type of error if that isn't the case.

answered Sep 19, 2012 at 11:35

Kerrek SB

480k96 gold badges904 silver badges1.1k bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Kerrek SB Over a year ago

@TheNewbie: Good stuff, I'm glad!

Some programmer dude · Accepted Answer · 2012-09-19 12:00:37Z

2

How about something like this:

for (int i = 0; i < sizeof(abyData) && (i * 2) < sByte.GetLength(); i++)
{
    char ch1 = sByte[i * 2];
    char ch2 = sByte[i * 2 + 1];

    int value = 0;

    if (std::isdigit(ch1))
        value += ch1 - '0';
    else
        value += (std::tolower(ch1) - 'a') + 10;

    // That was the four high bits, so make them that
    value <<= 4;

    if (std::isdigit(ch2))
        value += ch1 - '0';
    else
        value += (std::tolower(ch1) - 'a') + 10;

    abyData[i] = value;
}

Note: The code above is not tested.

edited Sep 19, 2012 at 12:00

answered Sep 19, 2012 at 11:32

Some programmer dude

411k36 gold badges420 silver badges655 bronze badges

Comments

Sdra · Accepted Answer · 2012-09-19 12:14:58Z

1

You could:

#include <stdint.h>
#include <sstream>
#include <iostream>

int main() {
    unsigned char result[8];
    std::stringstream ss;
    ss << std::hex << "0E00000000000400";
    ss >> *( reinterpret_cast<uint64_t *>( result ) );
    std::cout << static_cast<int>( result[1] ) << std::endl;
}

however take care of memory management issues!!! Plus the result is in the reverse order as you would expect, so:

result[0] = 0x00
result[1] = 0x04
...
result[7] = 0x0E

answered Sep 19, 2012 at 12:14

Sdra

2,37717 silver badges30 bronze badges

3 Comments

Kerrek SB Over a year ago

Why are there "memory management issues"? And why don't you mention that this code is undefined behaviour?

Neophile Over a year ago

This is not really that helpful when trying to do what I am intending to.

Sdra Over a year ago

@Kerrek SB: memory management issues can arise if the number of bytes required for the conversion do not match the size of result[]. Where is the undefined behaviour?

Collectives™ on Stack Overflow

CString Hex value conversion to Byte Array

3 Answers 3

1 Comment

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related