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

 

C++

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Common mathematical functions

Functions
Basic operations
abs(int)labsllabsimaxabs (C++11) abs(float)fabs divldivlldivimaxdiv (C++11) fmod	remainder (C++11) remquo (C++11) fma (C++11) fmax (C++11) fmin (C++11) fdim (C++11) nannanfnanl (C++11)(C++11)(C++11)
Exponential functions
exp exp2 (C++11) expm1 (C++11)	log log10 log1p (C++11) log2 (C++11)
Power functions
sqrt cbrt (C++11)	hypot (C++11) pow
Trigonometric and hyperbolic functions
sin cos tan asin acos atan atan2	sinh cosh tanh asinh (C++11) acosh (C++11) atanh (C++11)

Error and gamma functions
erf (C++11) erfc (C++11)	lgamma (C++11) tgamma (C++11)
Nearest integer floating point operations
ceil floor roundlroundllround (C++11)(C++11)(C++11)	trunc (C++11) nearbyint (C++11) rintlrintllrint (C++11)(C++11)(C++11)
Floating point manipulation functions
ldexp scalbnscalbln (C++11)(C++11) ilogb (C++11) logb (C++11)	frexp modf nextafternexttoward (C++11)(C++11) copysign (C++11)
Classification/Comparison
fpclassify (C++11) isfinite (C++11) isinf (C++11) isnan (C++11) isnormal (C++11) signbit (C++11)	isgreater (C++11) isgreaterequal (C++11) isless (C++11) islessequal (C++11) islessgreater (C++11) isunordered (C++11)
Macro constants
HUGE_VALFHUGE_VALHUGE_VALL (C++11)(C++11) INFINITY (C++11) NAN (C++11) math_errhandlingMATH_ERRNOMATH_ERREXCEPT (C++11)	FP_NORMALFP_SUBNORMALFP_ZEROFP_INFINITEFP_NAN (C++11)(C++11)(C++11)(C++11)(C++11)

 

Defined in header <cmath>
float       fdim ( float x, float y );	(1)	(since C++11) (constexpr since C++23)
float       fdimf( float x, float y );	(2)	(since C++11) (constexpr since C++23)
double      fdim ( double x, double y );	(3)	(since C++11) (constexpr since C++23)
long double fdim ( long double x, long double y );	(4)	(since C++11) (constexpr since C++23)
long double fdiml( long double x, long double y );	(5)	(since C++11) (constexpr since C++23)
Promoted    fdim ( Arithmetic1 x, Arithmetic2 y );	(6)	(since C++11) (constexpr since C++23)

1-5) Returns the positive difference between x and y, that is, if x>y, returns x-y, otherwise (if x≤y), returns +0.

6) A set of overloads or a function template for all combinations of arguments of arithmetic type not covered by (1-5). 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>
#ifndef __GNUC__
#pragma STDC FENV_ACCESS ON
#endif
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)labsllabs (C++11)	computes absolute value of an integral value (\(\small{|x|}\)|x|) (function)
fmaxfmaxffmaxl (C++11)(C++11)(C++11)	larger of two floating-point values (function)