# fabs, fabsf, fabsl, fabsd32, fabsd64, fabsd128

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< c‎ | numeric‎ | math

Defined in header ``<math.h>`` |  |
float fabsf( float arg ); | (1) | (since C99)
double fabs( double arg ); | (2) |
long double fabsl( long double arg ); | (3) | (since C99)
_Decimal32 fabsd32( _Decimal32 arg ); | (4) | (since C23)
_Decimal64 fabsd64( _Decimal64 arg ); | (5) | (since C23)
_Decimal128 fabsd128( _Decimal128 arg ); | (6) | (since C23)
Defined in header ``<tgmath.h>`` |  |
#define fabs( arith ) | (7) | (since C99)

1-6) Computes the absolute value of a floating-point value arg.

The functions with decimal floating-point parameters are declared if and only if the implementation predefines `__STDC_IEC_60559_DFP__` (i.e. the implementation supports decimal floating-point numbers). | (since C23)

7) Type-generic macro: If the argument has type _Decimal128, _Decimal64, _Decimal32,(since C23)long double, double, or float, `fabsd128`, `fabsd64`, `fabsd32`,(since C23)`fabsl`, `fabs`, or `fabsf` is called, respectively. Otherwise, if the argument has integer type, `fabs` is called. Otherwise, if the argument is complex, then the macro invokes the corresponding complex function (cabsf, cabs, cabsl). Otherwise, the behavior is undefined.

### Parameters

arg | - | floating-point value
arith | - | floating-point or integer value

### Return value

If successful, returns the absolute value of arg (\(\small |arg| \)|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

Run this code

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

    #define PI 3.14159

    // This numerical integration assumes all area is positive.
    double integrate(double f(double),
                     double a, double b, // assume a < b
                     unsigned steps) // assume steps > 0
    {
        const double dx = (b - a) / steps;
        double sum = 0.0;
        for (double x = a; x < b; x += dx)
            sum += fabs(f(x));
        return dx * 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("Area under sin(x) in [-PI, PI] = %f\n", integrate(sin, -PI, PI, 5101));
    }

Output:

    fabs(+3) = 3.000000
    fabs(-3) = 3.000000
    fabs(-0) = 0.000000
    fabs(-Inf) = inf
    Area under sin(x) in [-PI, PI] = 4.000000

### References

- C23 standard (ISO/IEC 9899:2024):

  - 7.12.7.2 The fabs functions (p: TBD)

  - 7.25 Type-generic math <tgmath.h> (p: TBD)

  - F.10.4.2 The fabs functions (p: TBD)

- C17 standard (ISO/IEC 9899:2018):

  - 7.12.7.2 The fabs functions (p: 181)

  - 7.25 Type-generic math <tgmath.h> (p: 272-273)

  - F.10.4.2 The fabs functions (p: 382)

- 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)

  - F.10.4.2 The fabs functions (p: 524)

- 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)

  - F.9.4.2 The fabs functions (p: 460)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 4.5.6.2 The fabs function

### See also

abslabsllabs (C99) | computes absolute value of an integral value (\(\small{|x|}\)|x|) (function)
copysigncopysignfcopysignl (C99)(C99)(C99) | produces a value with the magnitude of a given value and the sign of another given value (function)
signbit (C99) | checks if the given number is negative (function macro)
cabscabsfcabsl (C99)(C99)(C99) | computes the magnitude of a complex number (function)
C++ documentation for fabs

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