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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.

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



ANSI, Windows 95, Windows 98, Windows 98 Second Edition, Windows Millennium Edition, Windows Millennium Edition, Windows NT 4.0, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003

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
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