In C ++ when you write setprecision (12) for example 12 is in base 10, but when you write it as setprecision (012) it is an octal number, why?
Since constants with leading zeros (other than leading 0x) are always octal:
A cyclic integer literal (base eight) starts at 0 and consists of a sequence of octal digits.
C ++ Draft Standard ( n1905 ) §2.13.1
It has nothing to do with setprecision.
Since this worked in C. Back, when C was designed, octal numbers were often used, so they put a notation in them. Currently, he rarely helps and is mostly confusing.
In C ++, if an integer literal starts with a digit 0 (and 0 does not follow for x ), the following digits are treated as octal digits.
0
x