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Serial.print as HEX should ALWAYS print 2 chars per byte; it omits leading zeroes [imported] #40
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the thread on http://forum.arduino.cc//index.php?topic=179111.0 has some idears for this call
in particular, the changes I listed here
http://forum.arduino.cc//index.php?topic=179111.msg1385295#msg1385295based on my altered code found last posted here
http://forum.arduino.cc//index.php?topic=179111.msg1334253#msg1334253gives you the insight to a working solution, that fits in easily.
Changing the default behaviour of Print(..., HEX) is a backward incompatible change, it will suddenly break all existing sketches that relies on the current behaviour of Print (i.e. to print just the HEX value without leading zeros). Just this argument is enough to mark this issue as wont-fix.
Moreover, printing the leading zeros may be good for some kind of applications but not for others... what if I really want to print just the single hex number without the leading zero?
Printing a hex byte without the leading zero doesn't even make sense.
If you want that, you want a print nybble function.
At minimum, there needs to be a way to format hex data in the correct manner, right now we're stuck with an intermediate
snprintf().Reacted by Chris De Pasquale and Raffzahnif HEX is an ENUM
can't they just ad: HEX_LEADINGZERO to the enum and make every call to Serial.print(hexVal,HEX_LEADINGZERO) return a HEX format with leading zero...?Reacted by NajamELM- linked a pull request that will close this issueAdd Serial.print(foo, HEX_LEADINGZERO) #279
on Sep 2, 2026 - linked a pull request that will close this issueMake Serial.print(foo, HEX) ALWAYS print 2 chars per byte #280
on Sep 3, 2026
This is Issue 1097 moved from a Google Code project.
Added by 2012-11-05T10:22:49.000Z by dale.cal...@gmail.com.
Please review that bug for more context and additional comments, but update this bug.
Describe the request
Ensure
Printclass function output always has two characters per byte whenHEXbase is used.Describe the current behavior
Upload the following sketch to a board:
🙁
Fis printed in Serial Monitor instead of the expected0F.The output for HEX should always be one char per nibble; leading zeroes matter. For example this sketch:
Will output
0xF0FOinstead of the intended0x0F00FO. In this example, the value is totally changed by omission of the leading zero.arduino/ArduinoCore-API version
Arduino IDE 1.0.1, Duemilanove
Additional context
I can't think of any reason to omit leading zeroes when using the HEX format. In cases like this, where a sequence of bytes is read from a device that represents a multi-byte return value, and you want to see the real value returned it gives incorrect results. One could assemble the bytes into a LONG and then call the function, but I think that most who use the HEX format would like to see all their nibble values with any size data.
The example in the Arduino Language Reference sidesteps the issue by not using a value that would require a leading zero ;-)
https://docs.arduino.cc/language-reference/en/functions/communication/serial/print/
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