floor, floorf, floorl

Defined in header <math.h>
float       floorf( float arg );
(1) (since C99)
double      floor( double arg );
long double floorl( long double arg );
(3) (since C99)
Defined in header <tgmath.h>
#define floor( arg )
(4) (since C99)
1-3) Computes the largest integer value not greater than arg.
4) Type-generic macro: If arg has type long double, floorl is called. Otherwise, if arg has integer type or the type double, floor is called. Otherwise, floorf is called.


arg - floating point value

Return value

If no errors occur, the largest integer value not greater than arg, that is ⌊arg⌋, is returned.

Return value

Error handling

Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

  • The current rounding mode has no effect.
  • If arg is ±∞, it is returned, unmodified
  • If arg is ±0, it is returned, unmodified
  • If arg is NaN, NaN is returned


FE_INEXACT may be (but isn't required to be) raised when rounding a non-integer finite value.

The largest representable floating-point values are exact integers in all standard floating-point formats, so this function never overflows on its own; however the result may overflow any integer type (including intmax_t), when stored in an integer variable.


#include <math.h>
#include <stdio.h>
int main(void)
    printf("floor(+2.7) = %+.1f\n", floor(2.7));
    printf("floor(-2.7) = %+.1f\n", floor(-2.7));
    printf("floor(-0.0) = %+.1f\n", floor(-0.0));
    printf("floor(-Inf) = %+f\n",   floor(-INFINITY));

Possible output:

floor(+2.7) = +2.0
floor(-2.7) = -3.0
floor(-0.0) = -0.0
floor(-Inf) = -inf


  • C11 standard (ISO/IEC 9899:2011):
    • The floor functions (p: 251)
    • 7.25 Type-generic math <tgmath.h> (p: 373-375)
    • F.10.6.2 The floor functions (p: 526)
  • C99 standard (ISO/IEC 9899:1999):
    • The floor functions (p: 232)
    • 7.22 Type-generic math <tgmath.h> (p: 335-337)
    • F.9.6.2 The floor functions (p: 463)
  • C89/C90 standard (ISO/IEC 9899:1990):
    • The floor function

See also

computes smallest integer not less than the given value
rounds to nearest integer not greater in magnitude than the given value
rounds to nearest integer, rounding away from zero in halfway cases
C++ documentation for floor

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.