function
<ios> <iostream>

std::scientific

ios_base& scientific (ios_base& str);
Use scientific floating-point notation
Sets the floatfield format flag for the str stream to scientific.

When floatfield is set to scientific, floating-point values are written using scientific notation: the value is represented always with only one digit before the decimal point, followed by the decimal point and as many decimal digits as the precision field (precision). Finally, this notation always includes an exponential part consisting on the letter e followed by an optional sign and three exponential digits.

The floatfield format flag is both a selective and a toggle flag: it can take one or more of the following values:

flag valueeffect when set
fixedwrite floating-point values in fixed-point notation
scientificwrite floating-point values in scientific notation.
(none)write floating-point values in default floating-point notation.
The default notation (none) is a different floatfield value than either fixed or scientific. The default notation can be selected by calling str.unsetf(ios_base::floatfield).

For standard streams, no floatfield is set on initialization (default notation).
The floatfield format flag is both a selective and a toggle flag: it can take any of the following values, or none:

flag valueeffect when set
fixedwrite floating-point values in fixed-point notation.
scientificwrite floating-point values in scientific notation.
hexfloatwrite floating-point values in hexadecimal format.
The value of this is the same as (fixed|scientific)
defaultfloatwrite floating-point values in default floating-point notation. This is the value by default (same as none, before any other floatfield bit is set).

For standard streams, the floatfield format flag is set to defaultfloat on initialization.

The precision field can be modified using member precision.

Notice that the treatment of the precision field differs between the default floating-point notation and the fixed and scientific notations (see precision). On the default floating-point 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 field specifies exactly how many digits to display after the decimal point, even if they are trailing decimal zeros.

Parameters

str
Stream object whose floatfield format flag is affected.
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

Argument str.

Example

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
// modify floatfield
#include <iostream>     // std::cout, std::fixed, std::scientific

int main () {
  double a = 3.1415926534;
  double b = 2006.0;
  double c = 1.0e-10;

  std::cout.precision(5);

  std::cout << "default:\n";
  std::cout << a << '\n' << b << '\n' << c << '\n';

  std::cout << '\n';

  std::cout << "fixed:\n" << std::fixed;
  std::cout << a << '\n' << b << '\n' << c << '\n';

  std::cout << '\n';

  std::cout << "scientific:\n" << std::scientific;
  std::cout << a << '\n' << b << '\n' << c << '\n';
  return 0;
}


Possible output:
default:
3.1416
2006
1e-010

fixed:
3.14159
2006.00000
0.00000

scientific:
3.14159e+000
2.00600e+003
1.00000e-010

Data races

Modifies str. Concurrent access to the same stream object may cause data races.

Exception safety

Basic guarantee: if an exception is thrown, str is in a valid state.

See also