fmax, fmaxf, fmaxl

Defined in header <math.h>
float       fmaxf( float x, float y );
(1) (since C99)
double      fmax( double x, double y );
(2) (since C99)
long double fmaxl( long double x, long double y );
(3) (since C99)
Defined in header <tgmath.h>
#define fmax( x, y )
(4) (since C99)
1-3) Returns the larger of two floating point arguments, treating NaNs as missing data (between a NaN and a numeric value, the numeric value is chosen).
4) Type-generic macro: If any argument has type long double, fmaxl is called. Otherwise, if any argument has integer type or has type double, fmax is called. Otherwise, fmaxf is called.


x, y - floating point values

Return value

If successful, returns the larger of two floating point values. The value returned is exact and does not depend on any rounding modes.

Error handling

This function is not subject to any of the error conditions specified in math_errhandling.

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

  • If one of the two arguments is NaN, the value of the other argument is returned.
  • Only if both arguments are NaN is NaN returned.


This function is not required to be sensitive to the sign of zero, although some implementations additionally enforce that if one argument is +0 and the other is -0, then +0 is returned.


#include <stdio.h>
#include <math.h>
int main(void)
    printf("fmax(2,1)    = %f\n", fmax(2,1));
    printf("fmax(-Inf,0) = %f\n", fmax(-INFINITY,0));
    printf("fmax(NaN,-1) = %f\n", fmax(NAN,-1));


fmax(2,1)    = 2.000000
fmax(-Inf,0) = 0.000000
fmax(NaN,-1) = -1.000000


  • C17 standard (ISO/IEC 9899:2018):
    • The fmax functions (p: 188)
    • 7.25 Type-generic math <tgmath.h> (p: 397)
    • F.10.9.2 The fmax functions (p: 386)
  • C11 standard (ISO/IEC 9899:2011):
    • The fmax functions (p: 257-258)
    • 7.25 Type-generic math <tgmath.h> (p: 373-375)
    • F.10.9.2 The fmax functions (p: 530)
  • C99 standard (ISO/IEC 9899:1999):
    • The fmax functions (p: 238-239)
    • 7.22 Type-generic math <tgmath.h> (p: 335-337)
    • F.9.9.2 The fmax functions (p: 466)

See also

checks if the first floating-point argument is greater than the second
(function macro)
determines smaller of two floating-point values
C++ documentation for fmax

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