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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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frexp(3) Library Functions Manual frexp(3)
frexp, frexpf, frexpl - convert floating-point number to
fractional and integral components
Math library (libm, -lm)
#include <math.h>
double frexp(double x, int *e);
float frexpf(float x, int *e);
long double frexpl(long double x, int *e);
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 e.
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 e.
If x is a NaN, a NaN is returned, and the value of *e is
unspecified.
If x is positive infinity (negative infinity), positive infinity
(negative infinity) is returned, and the value of *e is
unspecified.
No errors occur.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ frexp(), frexpf(), frexpl() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
C11, POSIX.1-2008.
C99, POSIX.1-2001.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
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>
int
main(int argc, char *argv[])
{
double x, r;
int e;
x = strtod(argv[1], NULL);
r = frexp(x, &e);
printf("frexp(%g, &e) = %g: %g * %d^%d = %g\n", x, r, r, 2, e, x);
exit(EXIT_SUCCESS);
}
ldexp(3), modf(3)
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Linux man-pages 6.15 2025-07-19 frexp(3)
Pages that refer to this page: ldexp(3), modf(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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