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Test for not-a-number (NAN)
#include <math.h>
#define isnan ( x ) ...
- x
- The number you want to test.
libm
Use the -l m option to
qcc
to link against this library.
The isnan()
macro determines if x is Not-A-Number (NAN).
- 1
- The value of x is NAN.
- ≠ 1
- The value of x is a number.
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <inttypes.h>
#include <math.h>
#include <fpstatus.h>
int main(int argc, char** argv)
{
double a, b, c, d;
a = 2;
b = -0.5;
c = NAN;
fp_exception_mask(_FP_EXC_DIVZERO, 1);
d = 1.0/0.0;
printf("%f is %s \n", a,
(isnan(a)) ? "not a number" : "a number");
printf("%f is %s \n", b,
(isnan(b)) ? "not a number" : "a number");
printf("%f is %s \n", c,
(isnan(c)) ? "not a number" : "a number");
printf("%f is %s \n", d,
(isnan(d)) ? "not a number" : "a number");
return EXIT_SUCCESS;
}
produces the output:
2.000000 is a number
-0.500000 is a number
NAN is not a number
Inf is a number
POSIX 1003.1
Safety: | |
Cancellation point |
No |
Interrupt handler |
No |
Signal handler |
No |
Thread |
Yes |
isfinite(),
isinf()
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