Defined in header `<math.h>` | ||
---|---|---|

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) |

1-3) Computes the floating-point remainder of the division operation

`x/y`

.
4) Type-generic macro: If any argument has type

`long double`

, `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.

x, y | - | floating point values |

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.

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

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:

double fmod(double x, double y) { #pragma STDC FENV_ACCESS ON double result = remainder(fabs(x), (y = fabs(y))); if (signbit(result)) result += y; return copysign(result, x); }

#include <stdio.h> #include <math.h> #include <fenv.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 raised

- 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

(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` |

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