Defined in header <cmath>
float       ceil( float arg );
double      ceil( double arg );
long double ceil( long double arg );
double      ceil( Integral arg );
(4) (since C++11)
1-3) Computes the smallest integer value not less 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 smallest integer value not less 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.

This function (for double argument) behaves as if (except for the freedom to not raise FE_INEXACT) implemented by.

#include <cmath>
#include <cfenv>
double ceil(double x)
    double result;
    int save_round = std::fegetround();
    result = std::rint(x); // or std::nearbyint 
    return result;


#include <cmath>
#include <iostream>
int main()
    std::cout << std::fixed
              << "ceil(+2.4) = " << std::ceil(+2.4) << '\n'
              << "ceil(-2.4) = " << std::ceil(-2.4) << '\n'
              << "ceil(-0.0) = " << std::ceil(-0.0) << '\n'
              << "ceil(-Inf) = " << std::ceil(-INFINITY) << '\n';


ceil(+2.4) = 3.000000
ceil(-2.4) = -2.000000
ceil(-0.0) = -0.000000
ceil(-Inf) = -INF

See also

nearest integer not greater than the given value
nearest integer not greater in magnitude than the given value
nearest integer, rounding away from zero in halfway cases
nearest integer using current rounding mode
nearest integer using current rounding mode with
exception if the result differs
C documentation for ceil

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