isinf()

Updated: October 26, 2022

Test for infinity

Synopsis:

#include <math.h>

#define isinf ( x ) ...

Arguments:

x
The number that you want to test.

Library:

libm
The general-purpose math library.
libm-sve
(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:

Note: Compile your program with the -fno-builtin option to prevent the compiler from using a built-in version of the function.

Description:

The isinf() macro tests to see if a number is infinite.

Returns:

Nonzero
The value of x is infinity.
0
The value of x isn't infinity.

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,
           (isinf(a)) ? "infinite" : "not infinite");
    printf("%f is %s \n", b,
           (isinf(b)) ? "infinite" : "not infinite");
    printf("%f is %s \n", c,
           (isinf(c)) ? "infinite" : "not infinite");
    printf("%f is %s \n", d,
           (isinf(d)) ? "infinite" : "not infinite");

    return(0);
}

produces the output:

2.000000 is not infinite
-0.500000 is not infinite
nan is not infinite
inf is infinite

Classification:

C11, POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler Yes
Signal handler Yes
Thread Yes