FABS(3) Library Functions Manual FABS(3)

fabs fabsf fabsl — absolute value function

#include <math.h>

double fabs(double x);
float fabsf(float x);
long double fabsl(long double x);

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 (“POSIX.1”) defers to the ISO C standard.

These functions shall compute the absolute value of their argument x, | x |.

Upon successful completion, these functions shall return the absolute value of x.

If x is NaN, a NaN shall be returned.

If x is ±0, +0 shall be returned.

If x is ±Inf, +Inf shall be returned.

No errors are defined.

This example shows the use of fabs () to compute the 1-norm of a vector defined as follows:

norm1(v) = |v[0]| + |v[1]| + ... + |v[n-1]|

where | x | denotes the absolute value of x, n denotes the vector's dimension v [ i] denotes the i -th component of v (0<= i < n).

#include <math.h>


double
norm1(const double v[], const int n)
{
    int     i;
    double  n1_v;  /* 1-norm of v */


    n1_v = 0;
    for (i=0; i<n; i++) {
        n1_v += fabs (v[i]);
    }


    return n1_v;
}

None.

None.

None.

isnan(3), the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <math.h>

First released in Issue 1. Derived from Issue 1 of the SVID.

The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in the APPLICATION USAGE section.

The () and () functions are added for alignment with the ISO/IEC 9899:1999 (“ISO C99”) standard.

The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 (“ISO C99”) standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 (“ISO C99”) standard are marked.

IEEE Std 1003.1-2001 (“POSIX.1”)/Cor 2-2004, item XSH/TC2/D6/27 is applied, adding the example to the EXAMPLES section.

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January 1, 2004 posix.fail