awneil 
So <inttypes.h> defines macros for printf-style formats for printing the <stdint.h> types - uint8_t, etc.
https://en.wikibooks.org/wiki/C_Programming/inttypes.h
But there don't seem to be any for printing with leading zeros - eg, as with "%02X"
Am I missing something ... ?
EDIT
No, PRIX8 does not give leading zeros.
theusch 
Am I missing something ... ?
I think so. IME, printf formats are usually described (what reference are you using?) something like:
The format specifier string has the following structure:
%[flags][width][.precision][l]type_char
The optional flags characters are:
'-' left-justifies the result, padding on the right with spaces. If its not present, the result will be right-justified, padded on the left with zeros or spaces;
'+' signed conversion results will always begin with a '+' or '-' sign;
' ' if the value isn't negative, the conversion result will begin with a space. If the value is negative then it will begin with a '-' sign.
The optional width specifier sets the minimal width of an output value. If the result of the conversion is wider than the field width, the field will be expanded to accommodate the result, so not to cause field truncation.
The following width specifiers are supported:
n - at least n characters are outputted. If the result has less than n characters, then its field will be padded with spaces. If the '-' flag is used, the result field will be padded on the right, otherwise it will be padded on the left;
0n - at least n characters are outputted. If the result has less than n characters, it is padded on the left with zeros.
The optional precision specifier sets the maximal number of characters or minimal number of integer digits that may be outputted. ...
The 0n is independent from the type_char (x or X in your example).
Trix are for kids. PRIX are for quiche-eating politically-correct Generation-whatevers and not for real printf programmers.
No, PRIX8 does not give leading zeros.
"%02"PRIX8
clawson 
Isn't this why it's left for you to provide the %n bit ? The header only defines:
/** \ingroup avr_inttypes
decimal printf format for uint8_t */
#define PRIu8 "u"So presumably you can:
printf("%02" PRIu8, myu8Var);EDIT: must learn to copy/paste faster!
awneil The PRIX8 is only for the type. Additional formatting is done the "usual way":"%02"PRIX8
I thought I had tried that, but now I see that I had just put "%0"PRIX8 - I'd missed the width number!
Thanks to everyone for the answer - even though the forum only allows one to be marked as "the" (sic) solution.
awneil PRIX are for quiche-eating politically-correct Generation-whatevers and not for real printf programmers
theusch laugh
I'm just going by what I learnt from a master a few years ago:
printf() is a power tool and, like any power tool, is great when used properly - but can be unwieldy or even dangerous when used inappropriately and/or incorrectly.
https://www.avrfreaks.net/forum/...
Oh, wait, that was you...
[edit] LOL -- another pertinent fragment from that thread:
Real embedded programmers try to understand thoroughly all the implications including possible side effects of any library function (including printf()). This is supposed to be covered in painful details in the libraries'/toolchains' accompanying documentation. It is very, very rarely so. This why embedded programmers don't use printf().
And from a link in that thread:
Real programmers scorn floating point arithmetic. The decimal point was invented for pansy bedwetters who are unable to think big.