Fdim

Defined in header <cmath>.

Description

Returns the positive difference between x and y, that is, if x > y, returns x - y, otherwise (i.e. if x <= y) returns +0. The library provides overloads of std::fdim for all cv-unqualified floating-point types as the type of the parameters x and y.

Declarations

C++23

// 1)
constexpr /* floating-point-type */
            fdim ( /* floating-point-type */ x,
                   /* floating-point-type */ y );
// 2)
constexpr float       fdimf( float x, float y );
// 3)
constexpr long double fdiml( long double x, long double y );

Additional Overloads

// 4)
template< class Arithmetic1, class Arithmetic2 >
constexpr /* common-floating-point-type */ fdim( Arithmetic1 x, Arithmetic2 y );

C++11

// 1)
float       fdim ( float x, float y );
// 2)
double      fdim ( double x, double y );
// 3)
long double fdim ( long double x, long double y );
// 4)
float       fdimf( float x, float y );
// 5)
long double fdiml( long double x, long double y );

Additional Overloads

// 6)
template< class Arithmetic1, class Arithmetic2 >
/* common-floating-point-type */ fdim( Arithmetic1 x, Arithmetic2 y );

Parameters

x,y - floating-point or integer values

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.

The additional overloads are not required to be provided exactly as Additional Overloads. They only need to be sufficient to ensure that for their first argument num1 and second argument num2:

If num1 or num2 has type long double, then
std::fdim(num1, num2) has the same effect as
std::fdim(<a href='/docs/std/lang-support/static_cast'>static_cast</a>&lt;<span class='col-lb'>long double</span>&gt;(num1), <a href='/docs/std/lang-support/static_cast'>static_cast</a>&lt;<span class='col-lb'>long double</span>&gt;(num2)).

Otherwise, if num1 and/or num2 has type double or an integer type, then
std::fdim(num1, num2) has the same effect as
std::fdim(<a href='/docs/std/lang-support/static_cast'>static_cast</a>&lt;<span class='col-lb'>double</span>&gt;(num1), <a href='/docs/std/lang-support/static_cast'>static_cast</a>&lt;<span class='col-lb'>double</span>&gt;(num2)).

Otherwise, if num1 or num2 has type float, then
std::fdim(num1, num2) has the same effect as
std::fdim(<a href='/docs/std/lang-support/static_cast'>static_cast</a>&lt;<span class='col-lb'>float</span>&gt;(num1), <a href='/docs/std/lang-support/static_cast'>static_cast</a>&lt;<span class='col-lb'>float</span>&gt;(num2)).  (until C++23)

If num1 and num2 have arithmetic types, then
std::fdim(num1, num2) has the same effect as
std::fdim(static_cast</* common-floating-point-type */>(num1), static_cast</* common-floating-point-type */>(num2))

where /* common-floating-point-type */ is the floating-point type with the greatest floating-point conversion rank and greatest floating-point conversion subrank between the types of num1 and num2, arguments of integer type are considered to have the same floating-point conversion rank as double.

If no such floating-point type with the greatest rank and subrank exists, then overload resolution does not result in a usable candidate from the overloads provided.

Examples

#include <cerrno>
#include <cfenv>
#include <cmath>
#include <cstring>
#include <iostream>
 
#ifndef __GNUC__
#pragma STDC FENV_ACCESS ON
#endif
 
int main()
{
    std::cout 
        << "fdim(4, 1) = " 
        << std::fdim(4, 1) << '\n'
        << "fdim(1, 4) = " 
        << std::fdim(1, 4) << '\n'
        << "fdim(4,-1) = " 
        << std::fdim(4, -1) << '\n'
        << "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";
}

Result

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