C++, print floating-point number with precision, customise format

When we need to print a number with a specific format, such as printing it as a hexadecimal value or filling it with certain characters in front of it or some formatting options similar to the data format used in GLONASS (Global Navigation Satellite System) NAV DATA etc.
Ex we have some numbers

double a = 100.345;
double b = 2006.008;
double c = 2331.41592653498;

and we can show it look like :

0x64
_______+2006.01
2.331415927E+03

by using functions: setfill, setw, showbase, setprecision...from <iomanip>

cout <<left<<hex<<showbase << nouppercase << (long long)a << endl;
cout <<right<<setfill('_')<<fixed<<setw(15)<<setprecision(2)<<showpos << b << endl;
cout<<left<<scientific<<uppercase<<setprecision(9)<<noshowpos<<c << endl;