# std::fdim

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< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
float fdim( float x, float y ); | (1) | (since C++11)
double fdim( double x, double y ); | (2) | (since C++11)
long double fdim( long double x, long double y ); | (3) | (since C++11)
Promoted fdim( Arithmetic1 x, Arithmetic2 y ); | (4) | (since C++11)

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) A set of overloads or a function template for all combinations of arguments of arithmetic type not covered by 1-3). If any argument has integral type, it is cast to double. If any argument is long double, then the return type `Promoted` is also long double, otherwise the return type is always double.

### Parameters

x, y | - | values of floating-point or integral types

### 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 std::fmax(x-y, 0), except for the NaN handling requirements

### Example

Run this code

    #include <iostream>
    #include <cmath>
    #include <cerrno>
    #include <cstring>
    #include <cfenv>
    #pragma STDC FENV_ACCESS ON
    int main()
    {
        std::cout << "fdim(4, 1) = " << std::fdim(4, 1)
                  << " fdim(1, 4) = " << std::fdim(1, 4) << '\n'
                  << "fdim(4,-1) = " << std::fdim(4, -1)
                  << " fdim(1,-4) = " << std::fdim(1, -4) << '\n';
        // error handling
        errno=0; std::feclearexcept(FE_ALL_EXCEPT);
        std::cout << "fdim(1e308, -1e308) = " << std::fdim(1e308, -1e308) << '\n';
        if(errno == ERANGE)
            std::cout << "    errno == ERANGE: " << std::strerror(errno) << '\n';
        if(std::fetestexcept(FE_OVERFLOW))
            std::cout << "    FE_OVERFLOW raised\n";
    }

Output:

    fdim(4, 1) = 3 fdim(1, 4) = 0
    fdim(4,-1) = 5 fdim(1,-4) = 5
    fdim(1e308, -1e308) = inf
        errno == ERANGE: Numerical result out of range
        FE_OVERFLOW raised

### See also

abs(int)labs llabs (C++11) | computes absolute value of an integral value (|x|) (function)
fmax (C++11) | larger of two floating point values (function)
C documentation for fdim

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