Multiplies a floating-point number by an integral power of two.

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


Floating-point value.


Integer exponent.

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

For more information about errno and possible error return values, see errno, _doserrno, _sys_errlist, and _sys_nerr.

Because C++ allows overloading, you can call overloads of ldexp that take float or long double types. In a C program, ldexp always takes a double and an int and returns a double.


C header

C++ header

ldexp, ldexpf, ldexpl



For compatibility information, see Compatibility.

// 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