Defined in header <math.h>
#define isnormal(arg) /* implementation defined */
(since C99)

Determines if the given floating point number arg is normal, i.e. is neither zero, subnormal, infinite, nor NaN. The macro returns an integral value.

FLT_EVAL_METHOD is ignored: even if the argument is evaluated with more range and precision than its type, it is first converted to its semantic type, and the classification is based on that.


arg - floating point value

Return value

Nonzero integral value if arg is normal, ​0​ otherwise.


#include <stdio.h>
#include <math.h>
#include <float.h>
int main(void)
    printf("isnormal(NAN)         = %d\n", isnormal(NAN));
    printf("isnormal(INFINITY)    = %d\n", isnormal(INFINITY));
    printf("isnormal(0.0)         = %d\n", isnormal(0.0));
    printf("isnormal(DBL_MIN/2.0) = %d\n", isnormal(DBL_MIN/2.0));
    printf("isnormal(1.0)         = %d\n", isnormal(1.0));


isnormal(NAN)         = 0
isnormal(INFINITY)    = 0
isnormal(0.0)         = 0
isnormal(DBL_MIN/2.0) = 0
isnormal(1.0)         = 1


  • C11 standard (ISO/IEC 9899:2011):
    • The isnormal macro (p: 237)
  • C99 standard (ISO/IEC 9899:1999):
    • The isnormal macro (p: 217-218)

See also

classifies the given floating-point value
(function macro)
checks if the given number has finite value
(function macro)
checks if the given number is infinite
(function macro)
checks if the given number is NaN
(function macro)
C++ documentation for isnormal

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