Printing Leading Characters With Arduino IDE Serial Monitor

I have a blog post on calculating and checking the Cyclic Redundancy Check (CRC) byte when transmitting serial data. Here is a link. Near the bottom, is a sketch fragment of my CRC function and a table. The table illustrates how the CRC is calculated as the function progresses, bit, by bit, through the data. Here is the output I received from the Arduino IDE Serial Monitor:

Arduino IDE Serial Monitor Output Printing Binary Numbers

That's really ugly. The serial monitor that is part of the Arduino IDE does not print leading zeros. I wanted to see those zeros. "CRC" is an integer, so has 16 bits. "inByte[i]" is 8 bits long. I wrote a small function to calculate how many leading zeros to print when printing a binary number. Then, I expanded it to to handle numbers of any base, and finally, to add any leading character, not only zeros. This is the output using my leading character function:

Serial Monitor Output Using My Leading Character Function

My leading character function follows. It is amazingly simple. However, it's not universal. It does not handle minus signs or decimal points:

	void printleading(long to_print, int positions, int base, char chtr){
	double factor = pow(base, (positions -1));
	while ((to_print < factor) && (factor >= 1)){
	Serial.print(chtr);
	factor /= base;
	}
	}

view raw PrintLeadingCharacters.ino hosted with ❤ by GitHub

The "pow" operator raises the value in "base" to the power of "position" - 1. For example, if you wish to print a 16 bit binary number, "factor" will be 2¹⁵. You can see that "factor" can become a very large number, especially if you are dealing with decimal or hex numbers. Consequently, "factor" is a double, a floating point data type. However, the function may not work if "factor" wants to be too large. Just imagine if you wanted 16 characters of a decimal number. "factor" will be 1,000,000,000,000,000. A double data type for all Arduinos beside the Due is four bytes in length, not enough bytes to express 10¹⁵. The Due may be able to handle 10¹⁵ - it's double is 8 bytes in length.

Leading spaces can come in handy for printing dates. You can use it to line up dates like this:

• April   9, 2015
• April 10, 2015