Defined in header <cmath>
float       floor( float arg );
double      floor( double arg );
long double floor( long double arg );
double      floor( Integral arg );
(4) (since C++11)
1-3) Computes the largest integer value not greater than arg.
4) A set of overloads or a function template accepting an argument of any integral type. Equivalent to 2) (the argument is cast to double).


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 std::intmax_t), when stored in an integer variable.


#include <cmath>
#include <iostream>
int main()
    std::cout << std::fixed
              << "floor(+2.7) = " << std::floor(+2.7) << '\n'
              << "floor(-2.7) = " << std::floor(-2.7) << '\n'
              << "floor(-0.0) = " << std::floor(-0.0) << '\n'
              << "floor(-Inf) = " << std::floor(-INFINITY) << '\n';


floor(+2.7) = 2.000000
floor(-2.7) = -3.000000
floor(-0.0) = -0.000000
floor(-Inf) = -inf

See also

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

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