round, roundf, roundl


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The latest version of this topic can be found at round, roundf, roundl.

Rounds a floating-point value to the nearest integer.

double round(   
   double x   
float round(  
   float x  
);  // C++ only  
long double round(  
   long double x  
);  // C++ only  
float roundf(  
   float x  
long double roundl(  
   long double x  


The floating-point value to round.

The round functions return a floating-point value that represents the nearest integer to x. Halfway values are rounded away from zero, regardless of the setting of the floating-point rounding mode. There is no error return.

InputSEH ExceptionMatherr Exception

Because C++ allows overloading, you can call overloads of round that take and return float and long double values. In a C program, round always takes and returns a double.

RoutineRequired header
round, roundf, roundl<math.h>

For additional compatibility information, see Compatibility.

// crt_round.c  
// Build with: cl /W3 /Tc crt_round.c  
// This example displays the rounded results of  
// the floating-point values 2.499999, -2.499999,   
// 2.8, -2.8, 2.5 and -2.5.  
#include <math.h>  
#include <stdio.h>  
int main( void )  
   double x = 2.499999;  
   float y = 2.8f;  
   long double z = 2.5;  
   printf("round(%f) is %.0f\n", x, round(x));  
   printf("round(%f) is %.0f\n", -x, round(-x));  
   printf("roundf(%f) is %.0f\n", y, roundf(y));  
   printf("roundf(%f) is %.0f\n", -y, roundf(-y));  
   printf("roundl(%Lf) is %.0Lf\n", z, roundl(z));  
   printf("roundl(%Lf) is %.0Lf\n", -z, roundl(-z));  

round(2.499999) is 2  
round(-2.499999) is -2  
roundf(2.800000) is 3  
roundf(-2.800000) is -3  
roundl(2.500000) is 3  
roundl(-2.500000) is -3  


Floating-Point Support
ceil, ceilf, ceill
floor, floorf, floorl
fmod, fmodf
lrint, lrintf, lrintl, llrint, llrintf, llrintl
lround, lroundf, lroundl, llround, llroundf, llroundl
nearbyint, nearbyintf, nearbyintl
rint, rintf, rintl