std::fmod, std::fmodf, std::fmodl
| Defined in header <cmath>
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| (1) | ||
float fmod ( float x, float y ); double fmod ( double x, double y ); |
(until C++23) | |
| constexpr /* floating-point-type */ fmod ( /* floating-point-type */ x, |
(since C++23) | |
| float fmodf( float x, float y ); |
(2) | (since C++11) (constexpr since C++23) |
| long double fmodl( long double x, long double y ); |
(3) | (since C++11) (constexpr since C++23) |
| Additional overloads (since C++11) |
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| Defined in header <cmath>
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| template< class Integer > double fmod ( Integer x, Integer y ); |
(A) | (constexpr since C++23) |
std::fmod 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 treated as double.
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(since C++11) |
The floating-point remainder of the division operation x / y calculated by this function is exactly the value x - iquot * y, where iquot is x / y with its fractional part truncated.
The returned value has the same sign as x and is less than y in magnitude.
Contents |
Parameters
| x, y | - | floating-point or integer values |
Return value
If successful, returns the floating-point remainder of the division x / y as defined above.
If a domain error occurs, an implementation-defined value is returned (NaN where supported).
If a range error occurs due to underflow, the correct result (after rounding) is returned.
Error handling
Errors are reported as specified in math_errhandling.
Domain error may occur if y is zero.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
- If x is ±0 and y is not zero, ±0 is returned.
- If x is ±∞ and y is not NaN, NaN is returned and FE_INVALID is raised.
- If y is ±0 and x is not NaN, NaN is returned and FE_INVALID is raised.
- If y is ±∞ and x is finite, x is returned.
- If either argument is NaN, NaN is returned.
Notes
POSIX requires that a domain error occurs if x is infinite or y is zero.
std::fmod, but not std::remainder is useful for doing silent wrapping of floating-point types to unsigned integer types: (0.0 <= (y = std::fmod(std::rint(x), 65536.0)) ? y : 65536.0 + y) is in the range [-0.0, 65535.0], which corresponds to unsigned short, but std::remainder(std::rint(x), 65536.0 is in the range [-32767.0, +32768.0], which is outside of the range of signed short.
The double version of std::fmod behaves as if implemented as follows:
double fmod(double x, double y) { #pragma STDC FENV_ACCESS ON double result = std::remainder(std::fabs(x), y = std::fabs(y)); if (std::signbit(result)) result += y; return std::copysign(result, x); }
The expression x - std::trunc(x / y) * y may not equal std::fmod(x, y), when the rounding of x / y to initialize the argument of std::trunc loses too much precision (example: x = 30.508474576271183309, y = 6.1016949152542370172).
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:
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(until C++23) |
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If num1 and num2 have arithmetic types, then std::fmod(num1, num2) has the same effect as std::fmod(static_cast</* common-floating-point-type */>(num1), 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. |
(since C++23) |
Example
#include <cfenv> #include <cmath> #include <iostream> // #pragma STDC FENV_ACCESS ON int main() { std::cout << "fmod(+5.1, +3.0) = " << std::fmod(5.1, 3) << '\n' << "fmod(-5.1, +3.0) = " << std::fmod(-5.1, 3) << '\n' << "fmod(+5.1, -3.0) = " << std::fmod(5.1, -3) << '\n' << "fmod(-5.1, -3.0) = " << std::fmod(-5.1, -3) << '\n'; // special values std::cout << "fmod(+0.0, 1.0) = " << std::fmod(0, 1) << '\n' << "fmod(-0.0, 1.0) = " << std::fmod(-0.0, 1) << '\n' << "fmod(5.1, Inf) = " << std::fmod(5.1, INFINITY) << '\n'; // error handling std::feclearexcept(FE_ALL_EXCEPT); std::cout << "fmod(+5.1, 0) = " << std::fmod(5.1, 0) << '\n'; if (std::fetestexcept(FE_INVALID)) std::cout << " FE_INVALID raised\n"; }
Possible output:
fmod(+5.1, +3.0) = 2.1
fmod(-5.1, +3.0) = -2.1
fmod(+5.1, -3.0) = 2.1
fmod(-5.1, -3.0) = -2.1
fmod(+0.0, 1.0) = 0
fmod(-0.0, 1.0) = -0
fmod(5.1, Inf) = 5.1
fmod(+5.1, 0) = -nan
FE_INVALID raisedSee also
| (C++11) |
computes quotient and remainder of integer division (function) |
| (C++11)(C++11)(C++11) |
signed remainder of the division operation (function) |
| (C++11)(C++11)(C++11) |
signed remainder as well as the three last bits of the division operation (function) |
| C documentation for fmod
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