fmod, fmodf, fmodl
| Defined in header <math.h>
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||
| float fmodf( float x, float y ); |
(1) | (since C99) |
| double fmod( double x, double y ); |
(2) | |
| long double fmodl( long double x, long double y ); |
(3) | (since C99) |
| Defined in header <tgmath.h>
|
||
| #define fmod( x, y ) |
(4) | (since C99) |
fmodl is called. Otherwise, if any argument has integer type or has type double, fmod is called. Otherwise, fmodf is called.The floating-point remainder of the division operation x / y calculated by this function is exactly the value x - n * y, where n is x / y with its fractional part truncated.
The returned value has the same sign as x and is less or equal to y in magnitude.
Parameters
| x, y | - | floating-point 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.
fmod, but not remainder is useful for doing silent wrapping of floating-point types to unsigned integer types: (0.0 <= (y = fmod(rint(x), 65536.0 )) ? y : 65536.0 + y) is in the range [-0.0, 65535.0], which corresponds to unsigned short, but remainder(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 fmod behaves as if implemented as follows:
Example
#include <fenv.h> #include <math.h> #include <stdio.h> // #pragma STDC FENV_ACCESS ON int main(void) { printf("fmod(+5.1, +3.0) = %.1f\n", fmod(5.1, 3)); printf("fmod(-5.1, +3.0) = %.1f\n", fmod(-5.1, 3)); printf("fmod(+5.1, -3.0) = %.1f\n", fmod(5.1, -3)); printf("fmod(-5.1, -3.0) = %.1f\n", fmod(-5.1, -3)); // special values printf("fmod(+0.0, 1.0) = %.1f\n", fmod(0, 1)); printf("fmod(-0.0, 1.0) = %.1f\n", fmod(-0.0, 1)); printf("fmod(+5.1, Inf) = %.1f\n", fmod(5.1, INFINITY)); // error handling feclearexcept(FE_ALL_EXCEPT); printf("fmod(+5.1, 0) = %.1f\n", fmod(5.1, 0)); if (fetestexcept(FE_INVALID)) puts(" FE_INVALID raised"); }
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) = 0.0
fmod(-0.0, 1.0) = -0.0
fmod(+5.1, Inf) = 5.1
fmod(+5.1, 0) = nan
FE_INVALID raisedReferences
- C23 standard (ISO/IEC 9899:2024):
- 7.12.10.1 The fmod functions (p: TBD)
- 7.25 Type-generic math <tgmath.h> (p: TBD)
- F.10.7.1 The fmod functions (p: TBD)
- C17 standard (ISO/IEC 9899:2018):
- 7.12.10.1 The fmod functions (p: 185)
- 7.25 Type-generic math <tgmath.h> (p: 274-275)
- F.10.7.1 The fmod functions (p: 385)
- C11 standard (ISO/IEC 9899:2011):
- 7.12.10.1 The fmod functions (p: 254)
- 7.25 Type-generic math <tgmath.h> (p: 373-375)
- F.10.7.1 The fmod functions (p: 528)
- C99 standard (ISO/IEC 9899:1999):
- 7.12.10.1 The fmod functions (p: 235)
- 7.22 Type-generic math <tgmath.h> (p: 335-337)
- F.9.7.1 The fmod functions (p: 465)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.5.6.4 The fmod function
See also
| (C99) |
computes quotient and remainder of integer division (function) |
| (C99)(C99)(C99) |
computes signed remainder of the floating-point division operation (function) |
| (C99)(C99)(C99) |
computes signed remainder as well as the three last bits of the division operation (function) |
| C++ documentation for fmod
| |