How to initialize a float variable to be infinity in C language ？

Question

I want to initialize a variable in C language to be the plus infinity or minus infinity, how can I do that ? The below fails:

float plus_inf = 0.0/0.0;

score 9 · Accepted Answer · edited Jun 20 '20 at 09:12

9

You can try

#include <math.h>
....
float x = INFINITY;

According to the standard:

The macro

INFINITY

expands to a constant expression of type float representing positive or unsigned infinity, if available; else to a positive constant of type float that overflows at translation time.

edited Jun 20 '20 at 09:12

Community

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answered Apr 10 '15 at 10:12

AlexD

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Just a note: this requires C99 support. – Cong Ma Apr 10 '15 at 10:15
yes, thank you. but I have to use C89 in some platforms. – Ryan Apr 11 '15 at 16:58
For C89 use `HUGE_VAL` also from `` – mlel Oct 23 '18 at 15:10

David Ranieri · Answer 2 · 2015-04-10T10:22:01.340

2

0.0/0.0 is a nan (not a number), as an alternative to INFINITY (c89 and earlier) try:

float plus_inf = 1.0/0.0;

edited Apr 10 '15 at 10:22

answered Apr 10 '15 at 10:14

David Ranieri

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score 2 · Answer 3 · answered Apr 10 '15 at 10:18

2

Macro Infinity is defined under library.

float variable = INFINITY;

answered Apr 10 '15 at 10:18

How to initialize a float variable to be infinity in C language ？

3 Answers3