printf

copied from: https://cplusplus.com/reference/cstdio/printf/

syntax: %[flags][width][.precision][length]specifier

specifier Output Example
%d
%i		 Signed decimal integer 392
%u Unsigned decimal integer 7235
%o Unsigned octal 610
%x
%X		 Unsigned hexadecimal integer 7fa
7FA
%f
%F		 Decimal floating point 392.65
%e
%E		 Scientific notation (mantissa/exponent) 3.9265e+2
3.9265E+2
%g
%G		 Use the shortest representation: %e vs %f 392.65
%a
%A		 Hexadecimal floating point -0xc.90fep-2
%c Character a
%s String of characters sample
%p Pointer address b8000000
%n Nothing printed.
The corresponding argument must be a pointer to a signed int.
The number of characters written so far is stored in the pointed location.
%% A % followed by another % character will write a single % to the stream. %

example code example output
printf("Characters: %c %c \n", 'a', 65); Characters: a A
printf("Decimals: %d %ld\n", 1977, 650000L); Decimals: 1977 650000
printf("Preceding with blanks: %10d \n", 1977); Preceding with blanks: 1977
printf("Preceding with zeros: %010d \n", 1977); Preceding with zeros: 0000001977
printf("Some different radices: %d %x %o %#x %#o \n", 100, 100, 100, 100, 100); Some different radices: 100 64 144 0x64 0144
printf("floats: %4.2f %+.0e %E \n", 3.1416, 3.1416, 3.1416); floats: 3.14 +3e+000 3.141600E+000
printf("Width trick: %*d \n", 5, 10); Width trick: 10
printf("%s \n", "A string"); A string

flags description
- Left-justify within the given field width; Right justification is the default (see width sub-specifier).
+ Forces to preceed the result with a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded with a - sign.
(space) If no sign is going to be written, a blank space is inserted before the value.
# Used with o, x or X specifiers the value is preceeded with 0, 0x or 0X respectively for values different than zero.
Used with a, A, e, E, f, F, g, G it forces the written output to contain a decimal point even if no more digits follow. By default, if no digits follow, no decimal point is written.
0 Left-pads the number with zeroes (0) instead of spaces when padding is specified (see width sub-specifier).

width description
(number) Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger.
* The width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.

.precision description
.number For integer specifiers (d, i, o, u, x, X): precision specifies the minimum number of digits to be written. If the value to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer. A precision of 0 means that no character is written for the value 0.
For a, A, e, E, f, F specifiers: this is the number of digits to be printed after the decimal point (by default, this is 6).
For g and G specifiers: This is the maximum number of significant digits to be printed.
For s: this is the maximum number of characters to be printed. By default all characters are printed until the ending null character is encountered.
If the period is specified without an explicit value for precision, 0 is assumed.
.* The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.

strftime

copied from: https://cplusplus.com/reference/ctime/strftime/

Field type specifier Replaced by Example
year %C Year divided by 100 and truncated to integer (00-99) 20
%g Week-based year, last two digits (00-99) 01
%G Week-based year 2001
%y Year, last two digits (00-99) 01
%Y Year 2001
month %b Abbreviated month name Aug
%B Full month name * August
%h Abbreviated month name (same as %b) Aug
%m Month as a decimal number (01-12) 08
week %U Week number with the first Sunday as the first day of week one (00-53) 33
%V ISO 8601 week number (01-53) 34
%W Week number with the first Monday as the first day of week one (00-53) 34
day %d Day of the month, zero-padded (01-31) 23
%e Day of the month, space-padded ( 1-31) 23
%j Day of the year (001-366) 235
%a Abbreviated weekday name Thu
%A Full weekday name Thursday
%u ISO 8601 weekday as number with Monday as 1 (1-7) 4
%w Weekday as a decimal number with Sunday as 0 (0-6) 4
period %p AM or PM designation PM
hour %H Hour in 24h format (00-23) 14
%I Hour in 12h format (01-12) 02
%r 12-hour clock time 02:55:02 pm
%R 24-hour HH:MM time, equivalent to %H:%M 14:55
minute %M Minute (00-59) 55
second %S Second (00-61) 02
time zone %z ISO 8601 offset from UTC in timezone (1 minute=1, 1 hour=100)
If timezone cannot be determined, no characters		 +100
%Z Timezone name or abbreviation
If timezone cannot be determined, no characters		 CDT
shortcut %c Date and time representation Thu Aug 23 14:55:02 2001
%D Short MM/DD/YY date, equivalent to %m/%d/%y 08/23/01
%F Short YYYY-MM-DD date, equivalent to %Y-%m-%d 2001-08-23
%T ISO 8601 time format (HH:MM:SS), equivalent to %H:%M:%S 14:55:02
%x Date representation 08/23/01
%X Time representation 14:55:02
misc %n New-line character ('\n')
%t Horizontal-tab character ('\t')
%% A % sign %
E Uses the locale's alternative representation.
Applied to %Ec %EC %Ex %EX %Ey %EY
O Uses the locale's alternative numeric symbols.
Applied to %Od %Oe %OH %OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy

ISO 8601 & Unicode

copied from: https://unicode-org.github.io/icu/userguide/format_parse/datetime/

Format Pattern Result
"yyyy.MM.dd G 'at' HH:mm:ss zzz" "1996.07.10 AD at 15:08:56 PDT"
"EEE, MMM d, ''yy" "Wed, July 10, ‘96"
"h:mm a" "12:08 PM"
"hh 'o''clock' a, zzzz" "12 o’clock PM, Pacific Daylight Time"
"K:mm a, z" "0:00 PM, PST"
"yyyyy.MMMM.dd GGG hh:mm aaa" "01996.July.10 AD 12:08 PM"

Field type Symbol Meaning Pattern Example Output
era G era designator G, GG, or GGG
GGGG
GGGGG		 AD
Anno Domini
A
year y year yy
y or yyyy		 96
1996
Y year of “Week of Year” Y 1997
u extended year u 4601
U cyclic year name, as in Chinese lunar calendar U 甲子
r related Gregorian year r 1996
quarter Q quarter Q
QQ
QQQ
QQQQ
QQQQQ		 2
02
Q2
2nd quarter
2
q stand-alone quarter q
qq
qqq
qqqq
qqqqq		 2
02
Q2
2nd quarter
2
month M month in year M
MM
MMM
MMMM
MMMMM		 9
09
Sep
September
S
L stand-alone month in year L
LL
LLL
LLLL
LLLLL		 9
09
Sep
September
S
week w week of year w
ww		 27
27
W week of month W 2
day d day in month d
dd		 2
02
D day of year D 189
F day of week in month F 2 (2nd Wed in July)
g modified julian day g 2451334
E day of week E, EE, or EEE
EEEE
EEEEE
EEEEEE		 Tue
Tuesday
T
Tu
e local day of week
example: if Monday is 1st day, Tuesday is 2nd )		 e or ee
eee
eeee
eeeee
eeeeee		 2
Tue
Tuesday
T
Tu
c stand-alone local day of week c or cc
ccc
cccc
ccccc
cccccc		 2
Tue
Tuesday
T
Tu
period a am/pm marker a pm
hour h hour in am/pm (1~12) h
hh		 7
07
H hour in day (0~23) H
HH		 0
00
k hour in day (1~24) k
kk		 24
24
K hour in am/pm (0~11) K
KK		 0
00
minute m minute in hour m
mm		 4
04
second s second in minute s
ss		 5
05
S fractional second - truncates (like other time fields)
to the count of letters when formatting. Appends
zeros if more than 3 letters specified. Truncates at
three significant digits when parsing.		 S
SS
SSS
SSSS		 2
23
235
2350
A milliseconds in day A 61201235
time zone z Time Zone: specific non-location z, zz, or zzz
zzzz		 PDT
Pacific Daylight Time
Z Time Zone: ISO8601 basic hms / RFC 822
Time Zone: long localized GMT (=OOOO)
TIme Zone: ISO8601 extended hms (=XXXXX)		 Z, ZZ, or ZZZ
ZZZZ
ZZZZZ		 -0800
GMT-08:00
-08:00, -07:52:58, Z
O Time Zone: short localized GMT
Time Zone: long localized GMT (=ZZZZ)		 O
OOOO		 GMT-8
GMT-08:00
v Time Zone: generic non-location
(falls back first to VVVV)		 v
vvvv		 PT
Pacific Time or Los Angeles Time
V Time Zone: short time zone ID
Time Zone: long time zone ID
Time Zone: time zone exemplar city
Time Zone: generic location (falls back to OOOO)		 V
VV
VVV
VVVV		 uslax
America/Los_Angeles
Los Angeles
Los Angeles Time
X Time Zone: ISO8601 basic hm, with Z for 0
Time Zone: ISO8601 basic hm, with Z
Time Zone: ISO8601 extended hm, with Z
Time Zone: ISO8601 basic hms, with Z
Time Zone: ISO8601 extended hms, with Z		 X
XX
XXX
XXXX
XXXXX		 -08, +0530, Z
-0800, Z
-08:00, Z
-0800, -075258, Z
-08:00, -07:52:58, Z
x Time Zone: ISO8601 basic hm, without Z for 0
Time Zone: ISO8601 basic hm, without Z
Time Zone: ISO8601 extended hm, without Z
Time Zone: ISO8601 basic hms, without Z
Time Zone: ISO8601 extended hms, without Z		 x
xx
xxx
xxxx
xxxxx		 -08, +0530
-0800
-08:00
-0800, -075258
-08:00, -07:52:58
misc ' escape for text ' (nothing)
' ' two single quotes produce one ' ' ’