Determine if a number is finite
Synopsis:
#include <math.h>
int isfinite ( double x );
Arguments:
 x
 The number you want to test.
Library:
 libm
 The generalpurpose math library.
 libmsve
 (QNX Neutrino 7.1 or later)
A library that optimizes the code for ARMv8.2 chips that have Scalable Vector Extension hardware.
Your system requirements will determine how you should work with these libraries:
 If you want only selected processes to run with the SVE version, you can include both libraries in your OS image
and use the l m or l msve option to
qcc
to link explicitly against the appropriate one.
 If you want all processes to use the SVE version, include libmsve.so in your OS image
and set up a symbolic link from libm.so to libmsve.so.
Use the l m option to
qcc
to link against the library.
Note:
Compile your program with the fnobuiltin option to prevent the compiler from using a
builtin version of the function.
Description:
The isfinite() macro determines if x is finite.
Returns:
 Nonzero
 The value of x is finite.
 0
 The value of x is infinity or NaN.
Examples:
#include <stdio.h>
#include <math.h>
int main(int argc, char** argv)
{
double a, b, c, d;
a = 2;
b = 0.5;
c = NAN;
d = 1.0/0.0;
printf("%f is %s \n", a, (isfinite(a)) ? "finite" : "not finite");
printf("%f is %s \n", b, (isfinite(b)) ? "finite" : "not finite");
printf("%f is %s \n", c, (isfinite(c)) ? "finite" : "not finite");
printf("%f is %s \n", d, (isfinite(d)) ? "finite" : "not finite");
return(0);
}
produces the output:
2.000000 is finite
0.500000 is finite
nan is not finite
inf is not finite
Classification:
POSIX 1003.1
Safety: 

Cancellation point 
No 
Interrupt handler 
Yes 
Signal handler 
Yes 
Thread 
Yes 