frexp - Man Page

convert floating-point number to fractional and integral components


Math library (libm, -lm)


#include <math.h>

double frexp(double x, int *exp);
float frexpf(float x, int *exp);
long double frexpl(long double x, int *exp);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

frexpf(), frexpl():

    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE


These functions are used to split the number x into a normalized fraction and an exponent which is stored in exp.

Return Value

These functions return the normalized fraction. If the argument x is not zero, the normalized fraction is x times a power of two, and its absolute value is always in the range 1/2 (inclusive) to 1 (exclusive), that is, [0.5,1).

If x is zero, then the normalized fraction is zero and zero is stored in exp.

If x is a NaN, a NaN is returned, and the value of *exp is unspecified.

If x is positive infinity (negative infinity), positive infinity (negative infinity) is returned, and the value of *exp is unspecified.


No errors occur.


For an explanation of the terms used in this section, see attributes(7).

frexp(), frexpf(), frexpl()Thread safetyMT-Safe


C99, POSIX.1-2001, POSIX.1-2008.

The variant returning double also conforms to SVr4, 4.3BSD.


The program below produces results such as the following:

$ ./a.out 2560
frexp(2560, &e) = 0.625: 0.625 * 2^12 = 2560
$ ./a.out -4
frexp(-4, &e) = -0.5: -0.5 * 2^3 = -4

Program source

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

main(int argc, char *argv[])
    double x, r;
    int exp;

    x = strtod(argv[1], NULL);
    r = frexp(x, &exp);

    printf("frexp(%g, &e) = %g: %g * %d^%d = %g\n",
           x, r, r, FLT_RADIX, exp, x);

See Also

ldexp(3), modf(3)

Referenced By

ldexp(3), modf(3).

The man pages frexpf(3) and frexpl(3) are aliases of frexp(3).

2023-02-05 Linux man-pages 6.03