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

Determines if the given floating point number arg has finite value i.e. it is normal, subnormal or zero, but not infinite or 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 has finite value, ​0​ otherwise.


#include <stdio.h>
#include <math.h>
#include <float.h>
int main(void)
    printf("isfinite(NAN)         = %d\n", isfinite(NAN));
    printf("isfinite(INFINITY)    = %d\n", isfinite(INFINITY));
    printf("isfinite(0.0)         = %d\n", isfinite(0.0));
    printf("isfinite(DBL_MIN/2.0) = %d\n", isfinite(DBL_MIN/2.0));
    printf("isfinite(1.0)         = %d\n", isfinite(1.0));
    printf("isfinite(exp(800))    = %d\n", isfinite(exp(800)));

Possible output:

isfinite(NAN)         = 0
isfinite(INFINITY)    = 0
isfinite(0.0)         = 1
isfinite(DBL_MIN/2.0) = 1
isfinite(1.0)         = 1
isfinite(exp(800))    = 0


  • C11 standard (ISO/IEC 9899:2011):
    • The isfinite macro (p: 236)
  • C99 standard (ISO/IEC 9899:1999):
    • The isfinite macro (p: 216-217)

See also

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

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