spec    %#o     %#x     %#o     %#X     %.0d    %.2d    %-2d    
                arg     0       0       1       1       0       1       1       
C89     printf          0       0       01      0X1             01      1       
Go      fmt.Printf      0       0x0     01      0X1             01      1       
Py 2    print '...' %   0       0x0     01      0X1             01      1       
Py 3    print('...' %)  0o0     0x0     0o1     0X1     0       01      1       
Java 8  Sys.out.printf  00      0x0     01      0X1     (n/a)   (n/a)   1       
C++23   std::print      0       0x0     01      0X1     (n/a)   (n/a)    1      
Py 3    print(f'...')   0o0     0x0     0o1     0X1     (n/a)   (n/a)    1      
Rust    print!          0o0     0x0     0o1     0x1     0       1        1      

for Rust, {:.0}, {:.2} and {:-2} were used instead of {:.0d}, {:.2d} and {:-2d} because the latter don't compile.
for %.0d and %.2d, precisions on integral types, C++23, Python 3 and Java 8 error out while Rust ignores the precision

so my takeaways are:
- the '-' flag doesn't always denote left alignment and may turn out to be a silent no-op
- in C and C++, %#x and %#o may not output a prefix when the argument is zero, so avoid them for uniform output; for example, in C and C++, %#.2x and %#04x are likely bugged
- with integral types, default to zero-padding to a field width instead of using a precision, just because the latter is ill-supported; for example, default to %02x instead of %.2x
- ideally avoid the '#', '+' and ' ' flags when zero-padding an integral type to a field width, so the digit count matches the field width; for example, prefer 0x%02x and %#.2x to %#04x
- if you so wish, use precisions and field widths on integral types semantically; specifically, consider the output if the '#' flag were toggled or the argument were negative

documentation:
https://cplusplus.com/reference/cstdio/fprintf/
https://pkg.go.dev/fmt
https://docs.python.org/2/library/stdtypes.html#string-formatting
https://docs.python.org/3/library/stdtypes.html#old-string-formatting
https://docs.oracle.com/javase/8/docs/api/java/util/Formatter.html
https://en.cppreference.com/w/cpp/utility/format/spec
https://docs.python.org/3/library/string.html#formatspec
https://doc.rust-lang.org/std/fmt/index.html

https://zig.guide/standard-library/advanced-formatting/
https://github.com/ziglang/zig/issues/19488#issuecomment-2203005231

 vim:et:ts=8:sw=8: