function
<ios> <iostream>

std::defaultfloat

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

When floatfield is set to defaultfloat, floating-point values are written using the default notation: the representation uses as many meaningful digits as needed up to the stream's decimal precision (precision), counting both the digits before and after the decimal point (if any).

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 this value (defaultfloat) on initialization.

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

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// hexfloat floatfield
#include <iostream>     // std::cout, std::hexfloat, std::defaultfloat

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

  std::cout.precision(5);

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

  std::cout << '\n';

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

  return 0;
}


Possible output:
hexfloat:
0x1.921fb5p+1
0x1.f58000p+10
0x1.b7cdfep-34

defaultfloat:
3.14159
2006
1e-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

fixed
Use fixed floating-point notation (function )
scientific
Use scientific floating-point notation (function )
hexfloat
Use hexadecimal floating-point format (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 )

C++