NAME¶

std::fdim,std::fdimf,std::fdiml - std::fdim,std::fdimf,std::fdiml

Synopsis¶

Defined in header <cmath>
float fdim ( float x, float y );

double fdim ( double x, double y ); (until C++23)

long double fdim ( long double x, long double y );
constexpr /* floating-point-type */

fdim ( /* floating-point-type */ x, (since C++23)
(1)
/* floating-point-type */ y );
float fdimf( float x, float y ); (2) (since C++11)
(constexpr since C++23)
long double fdiml( long double x, long double y ); (3) (since C++11)
(constexpr since C++23)
Additional overloads (since C++11)
Defined in header <cmath>
template< class Integer > (A) (constexpr since C++23)
double fdim ( Integer x, Integer y );

1-3) 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.
(since C++23)

A) Additional overloads are provided for all integer types, which are (since C++11)
treated as double.

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 (A). 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(static_cast<long double>(num1),
static_cast<long double>(num2)).
* Otherwise, if num1 and/or num2 has type double or an integer type,
then std::fdim(num1, num2) has the same effect as (until C++23)
std::fdim(static_cast<double>(num1),
static_cast<double>(num2)).
* Otherwise, if num1 or num2 has type float, then std::fdim(num1,
num2) has the same effect as std::fdim(static_cast<float>(num1),
static_cast<float>(num2)).
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 (since C++23)
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.

Example¶

// Run this code

#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";
}

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 computes absolute value of an integral value (\(\small{|x|}\)|x|)
llabs (function)
(C++11)
fmax
fmaxf
fmaxl larger of two floating-point values
(C++11) (function)
(C++11)
(C++11)
C documentation for
fdim