frexp

Article
04/22/2008

Gets the mantissa and exponent of a floating-point number.

double frexp(
   double x,
   int *expptr 
);
float frexp(
   float x,
   int * expptr
);  // C++ only
long double frexp(
   long double x,
   int * expptr
);  // C++ only

Parameters

x
Floating-point value.
expptr
Pointer to stored integer exponent.

Return Value

frexp returns the mantissa. If x is 0, the function returns 0 for both the mantissa and the exponent. If expptr is NULL, the invalid parameter handler is invoked as described in Parameter Validation. If execution is allowed to continue, this function sets errno to EINVAL and returns 0.

Remarks

The frexp function breaks down the floating-point value (x) into a mantissa (m) and an exponent (n), such that the absolute value of m is greater than or equal to 0.5 and less than 1.0, and x = m*2ⁿ. The integer exponent n is stored at the location pointed to by expptr.

C++ allows overloading, so you can call overloads of frexp. In a C program, frexp always takes a double and an integer and returns a double.

Requirements

Function	Required header
frexp	<math.h>

For additional compatibility information, see Compatibility in the Introduction.

Example

// crt_frexp.c
// This program calculates frexp( 16.4, &n )
// then displays y and n.
 

#include <math.h>
#include <stdio.h>

int main( void )
{
   double x, y;
   int n;

   x = 16.4;
   y = frexp( x, &n );
   printf( "frexp( %f, &n ) = %f, n = %d\n", x, y, n );
}

frexp( 16.400000, &n ) = 0.512500, n = 5

.NET Framework Equivalent

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.

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