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 combine one or more of the following values:
| flag value | effect when set |
|---|
| fixed | write floating-point values in fixed-point notation |
| scientific | write 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 value | effect when set |
|---|
| fixed | write floating-point values in fixed-point notation. |
| scientific | write floating-point values in scientific notation. |
| hexfloat | write floating-point values in hexadecimal format.
The value of this is the same as (fixed|scientific) |
| defaultfloat | write 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.