fabs

float       fabsf( float arg );

double      fabs( double arg );

long double fabsl( long double arg );

#define fabs( arg )

Parameters

Return value

If successful, returns the absolute value of arg (|arg|). The value returned is exact and does not depend on any rounding modes.

Error handling

This function is not subject to any of the error conditions specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

• If the argument is ±0, +0 is returned
• If the argument is ±∞, +∞ is returned
• If the argument is NaN, NaN is returned

Example

#include <stdio.h>
#include <math.h>
 
/* This numerical integration assumes all area is positive. */
#define PI 3.14159
double num_int (double a, double b,
                double f(double),
                unsigned n) {
    if (a == b) return 0.0;
    if (n == 0) n=1;   /* avoid division by zero */
    double h = (b-a)/n;
    double sum = 0.0;
    for (unsigned k=0; k < n; ++k)
        sum += h*fabs(f(a+k*h));
    return sum;
}
 
int main(void)
{
    printf("fabs(+3) = %f\n", fabs(+3.0));
    printf("fabs(-3) = %f\n", fabs(-3.0));
    // special values
    printf("fabs(-0) = %f\n", fabs(-0.0));
    printf("fabs(-Inf) = %f\n", fabs(-INFINITY));
 
    printf("%f\n", num_int(0.0,2*PI,sin,100000));
 
}

fabs(+3) = 3.000000
fabs(-3) = 3.000000
fabs(-0) = 0.000000
fabs(-Inf) = inf
4.000000

References

• C11 standard (ISO/IEC 9899:2011):
  • 7.12.7.2 The fabs functions (p: 248)
  • 7.25 Type-generic math <tgmath.h> (p: 373-375)
• C99 standard (ISO/IEC 9899:1999):
  • 7.12.7.2 The fabs functions (p: 228-229)
  • 7.22 Type-generic math <tgmath.h> (p: 335-337)
• C89/C90 standard (ISO/IEC 9899:1990):
  • 4.5.6.2 The fabs function

See also