C++/CLI Convert String^ to array of bytes

Question

I am using Windows Forms C++/CLI and have a function that calls a Python script which returns a string representation of bytes. I would like to convert the string to an array of bytes.

For example:

String^ demoString = "09153a"; // example of data returned from Python script

array<Byte>^ bytes;
    
// This is what I tried but does not give me the output I want
bytes = System::Text::Encoding::UTF8->GetBytes(demoString);

unsigned char zero = bytes[0];
unsigned char one = bytes[1];
unsigned char two = bytes[2];
unsigned char three = bytes[3];

this->richTextBox1->Text += zero + "\n";
this->richTextBox1->Text += one + "\n";
this->richTextBox1->Text += two + "\n";
this->richTextBox1->Text += three + "\n";

What this ends up printing to the text box is the decimal representation of the ascii characters:

What I am trying to get is an array with the values {0x09, 0x15, 0x3a};

wohlstad · Accepted Answer · 2022-10-26 07:16:38Z

You need a function to parse the hex string by splitting it into pairs, and then converting every pair of hex characters into a byte value.

You can see a complete example below using a console application.

Note: your hex string "09153a" represents only 3 bytes (so only zero, one, two are relevant).

using namespace System;

array<Byte>^ ParseBytes(String^ str)
{
    if (str->Length % 2 != 0)
    {
        return nullptr;
    }
    int numBytes = str->Length / 2;
    array<Byte>^ bytes = gcnew array<Byte>(numBytes);
    for (int i = 0; i < numBytes; ++i)
    {
        String^ byteStr = str->Substring(i * 2, 2);
        if (!Byte::TryParse(byteStr, Globalization::NumberStyles::HexNumber, nullptr, bytes[i]))
        {
            return nullptr;
        }
    }
    return bytes;
}

int main(array<System::String ^> ^args)
{
    String^ demoString = "09153a"; // example of data returned from Python script

    array<Byte>^ bytes = ParseBytes(demoString);

    Byte zero = bytes[0];
    Byte one = bytes[1];
    Byte two = bytes[2];

    Console::WriteLine("Hex: 0x" + zero.ToString("X2"));
    Console::WriteLine("Hex: 0x" + one.ToString("X2"));
    Console::WriteLine("Hex: 0x" + two.ToString("X2"));

    return 0;
}

Output:

Hex: 0x09
Hex: 0x15
Hex: 0x3A

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