# fdim

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< c‎ | numeric‎ | math

Defined in header `<math.h>` |  |
float fdimf( float x, float y ); | (1) | (since C99)
double fdim( double x, double y ); | (2) | (since C99)
long double fdiml( long double x, long double y ); | (3) | (since C99)
Defined in header `<tgmath.h>` |  |
#define fdim( x, y ) | (4) | (since C99)

1-3) Returns the positive difference between x and y, that is, if x>y, returns x-y, otherwise (if x≤y), returns +0.
4) Type-generic macro: If any argument has type long double, `fdiml` is called. Otherwise, if any argument has integer type or has type double, `fdim` is called. Otherwise, `fdimf` is called.

### Parameters

x, y | - | floating point value

### Return value

If successful, returns the positive difference between x and y.

If a range error due to overflow occurs, `+HUGE_VAL`, `+HUGE_VALF`, or `+HUGE_VALL` is returned.

If a range error due to underflow occurs, the correct value (after rounding) is returned.

### Error handling

Errors are reported as specified in math_errhandling.

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

- If either argument is NaN, NaN is returned

### Notes

Equivalent to fmax(x-y, 0) except for the NaN handling requirements.

### Example

Run this code

    #include <stdio.h>
    #include <math.h>
    #include <errno.h>
    #include <fenv.h>
    #pragma STDC FENV_ACCESS ON
    int main(void)
    {
        printf("fdim(4, 1) = %f, fdim(1, 4)=%f\n", fdim(4,1), fdim(1,4));
        printf("fdim(4,-1) = %f, fdim(1,-4)=%f\n", fdim(4,-1), fdim(1,-4));
        //error handling
        errno = 0; feclearexcept(FE_ALL_EXCEPT);
        printf("fdim(1e308, -1e308) = %f\n", fdim(1e308, -1e308));
        if(errno == ERANGE) perror("    errno == ERANGE");
        if(fetestexcept(FE_OVERFLOW)) puts("    FE_OVERFLOW raised");
    }

Possible output:

    fdim(4, 1) = 3.000000, fdim(1, 4)=0.000000
    fdim(4,-1) = 5.000000, fdim(1,-4)=5.000000
    fdim(1e308, -1e308) = inf
        errno == ERANGE: Numerical result out of range
        FE_OVERFLOW raised

### References

- C11 standard (ISO/IEC 9899:2011):

  - 7.12.12.1 The fdim functions (p: 257)

  - 7.25 Type-generic math <tgmath.h> (p: 373-375)

  - F.10.9.1 The fdim functions (p: 530)

- C99 standard (ISO/IEC 9899:1999):

  - 7.12.12.1 The fdim functions (p: 238)

  - 7.22 Type-generic math <tgmath.h> (p: 335-337)

  - F.9.9.1 The fdim functions (p: 466)

### See also

abs labs llabs (C99) | computes absolute value of an integral value (|x|) (function)
fmax fmaxf fmaxl (C99)(C99)(C99) | determines larger of two floating-point values (function)
C++ documentation for fdim

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