# undefined reference to acosf



## graudeejs (Sep 23, 2012)

Today I was refreshing my little c knowledge, and I failed to compile simple app with


> undefined reference to `acosf`


I got math.h included. compiling with -std=c99. Why is it failing? I checked math.h source it has


```
/* float versions of ANSI/POSIX functions */
#if __ISO_C_VISIBLE >= 1999
float	acosf(float);
...
```

So why isn't acosf defined? (How to solve this correctly?)


EDIT:
fount it... heck I was missig *-lm* linker switch


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