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Computes a real number from the mantissa and exponent.

double ldexp(
   double x,
   int exp 
float ldexp(
   float x,
   int exp
);  // C++ only
long double ldexp(
   long double x,
   int exp
);  // C++ only


Floating-point value.
Integer exponent.

Return Value

The ldexp function returns the value of x * 2exp if successful. On overflow (depending on the sign of x), ldexp returns +/– HUGE_VAL; the errno variable is set to ERANGE.

See _doserrno, errno, _sys_errlist, and _sys_nerr for more information on this, and other, return codes.


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


Routine Required header Compatibility
ldexp <math.h> ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP

For additional compatibility information, see Compatibility in the Introduction.


All versions of the C run-time libraries.


// crt_ldexp.c

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

int main( void )
   double x = 4.0, y;
   int p = 3;

   y = ldexp( x, p );
   printf( "%2.1f times two to the power of %d is %2.1f\n", x, p, y );


4.0 times two to the power of 3 is 32.0

See Also

Floating-Point Support | frexp | modf | Run-Time Routines and .NET Framework Equivalents

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