Append Char To StringBuilder C++/CLI

Question

I am trying to use StringBuilder to create the output that is being sent over the serial port for a log file. The output is stored in a byte array, and I am recursing through it.

ref class UART_G {
   public:
     static array<System::Byte>^ message = nullptr;
     static uint8_t message_length = 0;
};

static void logSend ()
{
  StringBuilder^ outputsb = gcnew StringBuilder();
  outputsb->Append("Sent ");
  for (uint8_t i = 0; i < UART_G::message_length; i ++)
  {
    unsigned char mychar = UART_G::message[i];
    if (
      (mychar >= ' ' && mychar <= 'Z') || //Includes 0-9, A-Z.
      (mychar >= '^' && mychar <= '~') || //Includes a-z.
      (mychar >= 128 && mychar <= 254)) //I think these are okay.
    {
      outputsb->Append(L""+mychar);
    }
    else
    {
      outputsb->Append("[");
      outputsb->Append(mychar);
      outputsb->Append("]");
    }
  }
  log_line(outputsb->ToString());
}

I want all plain text characters (eg A, :) to be sent as text, while functional characters (eg BEL, NEWLINE) will be sent like [7][13].

What is happening is that the StringBuilder, in all cases, is outputting the character as a number. For example, A is being sent out as 65.

For example, if I have the string 'APPLE' and a newline in my byte array, I want to see:

Sent APPLE[13]

Instead, I see:

Sent 6580807669[13]

I have tried every way imaginable to get it to display the character properly, including type-casting, concatenating it to a string, changing the variable type, etc... I would really appreciate if anyone knows how to do this. My log files are largely unreadable without this function.

Answer 1

You're getting the ASCII values because the compiler is choosing one of the Append overloads that takes an integer of some sort. To fix this, you could do a explicit cast to System::Char, to force the correct overload.

However, that won't necessarily give the proper results for 128-255. You could cast a value in that range from Byte to Char, and it'll give something, but not necessarily what you expect. First off, 0x80 through 0x9F are control characters, and whereever you're getting the bytes from might not intend the same representation for 0xA0 through 0xFF as Unicode has.

In my opinion, the best solution would be to use the "[value]" syntax that you're using for the other control characters for 0x80 through 0xFF as well. However, if you do want to convert those to characters, I'd use Encoding::Default, not Encoding::ASCII. ASCII only defines 0x00 through 0x7F, 0x80 and higher will come out as "?". Encoding::Default is whatever code page is defined for the language you have selected in Windows.

Combine all that, and here's what you'd end up with:

for (uint8_t i = 0; i < UART_G::message_length; i ++)
{
  unsigned char mychar = UART_G::message[i];

  if (mychar >= ' ' && mychar <= '~' && mychar != '[' && mychar != ']')
  {
    // Use the character directly for all ASCII printable characters, 
    // except '[' and ']', because those have a special meaning, below.
    outputsb->Append((System::Char)(mychar));
  }
  else if (mychar >= 128)
  {
    // Non-ASCII characters, use the default encoding to convert to Unicode.
    outputsb->Append(Encoding::Default->GetChars(UART_G::message, i, 1));
  }
  else
  {
    // Unprintable characters, use the byte value in brackets.
    // Also do this for bracket characters, so there's no ambiguity 
    // what a bracket means in the logs. 
    outputsb->Append("[");
    outputsb->Append((unsigned int)mychar);
    outputsb->Append("]");
  }
}

Answer 2

You are recieveing ascii value of the string .

See the Ascii chart

 65 = A
 80 = P
 80 = P
 76 = L
 69 = E

Just write a function that converts the ascii value to string

Answer 3

Here is the code I came up with which resolved the issue:

static void logSend ()
{
  StringBuilder^ outputsb = gcnew StringBuilder();
  ASCIIEncoding^ ascii = gcnew ASCIIEncoding;
  outputsb->Append("Sent ");
  for (uint8_t i = 0; i < UART_G::message_length; i ++)
  {
    unsigned char mychar = UART_G::message[i];
    if (
      (mychar >= ' ' && mychar <= 'Z') || //Includes 0-9, A-Z.
      (mychar >= '^' && mychar <= '~') || //Includes a-z.
      (mychar >= 128 && mychar <= 254)) //I think these are okay.
    {
      outputsb->Append(ascii->GetString(UART_G::message, i, 1));
    }
    else
    {
      outputsb->Append("[");
      outputsb->Append(mychar);
      outputsb->Append("]");
    }
  }
  log_line(outputsb->ToString());
}

I still appreciate any alternatives which are more efficient or simpler to read.