When floatfield is set to fixed, float values are written using fixedpoint notation, which means the value is represented with exactly as many digits in the fraction part as specified by the precision field and with no exponent part.
The floatfield format flag is both a selective and a toggle flag, so it can take any of its two possible following values (using the manipulators fixed and scientific), or none of them (using ios_base::unsetf):
flag value  effect when set 

fixed  write floating point values in fixedpoint notation. 
scientific  write floatingpoint values in scientific notation. 
(none)  write floatingpoint values in default floatingpoint notation. 
The floatfield flag is not set in standard streams on initialization.
The precision field can be modified using the ios_base::precision member of the stream.
Notice that the treatment of the precision field differs between the default floatingpoint notation and the fixed and scientific notations. On the default floatingpoint notation, the precision field specifies the maximum number of meaningful digits to display both before and after the decimal point, while in both the fixed and scientific notations, the precision filed specifies exactly how many digits to display after the decimal point, even if they are trailing decimal zeros.
Parameters
 str
 Stream object where to apply.
Because this function is a manipulator, it is designed to be used alone with no arguments in conjunction with the insertion (<<) and extraction (>>) operations on streams (see example below).
Return Value
A reference to the stream object.Example
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 

The execution of this example displays something similar to:
3.1416 2006 1e010 3.14159 2006.00000 0.00000 3.14159e+000 2.00600e+003 1.00000e010 
See also
scientific  Use scientific notation (manipulator function) 
ios_base::flags  Get/set format flags (public member function) 
ios_base::setf  Set specific format flags (public member function) 
ios_base::unsetf  Clear specific format flags (public member function) 