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## Re: can't find ceil function in math library

**From**: |
Ingo Krabbe |

**Subject**: |
Re: can't find ceil function in math library |

**Date**: |
Thu, 3 Jul 2014 14:01:59 +0200 |

Actually it makes not much sense to ask about why autoconf a/o libtool does
this or that, as the tools themselves are coded beyond understanding or
readability. They just do on some systems what they are expected to do.
Of course AC_CHECK_LIB([m],[main]), shouldn't return true as main is no member
of libm. On the other hand AC_CHECK_LIB or other AC macros aren't meant to be
tested against transzendental usage and it should be quite clear by definition
that main is not part of the true set of AC_CHECK_LIB([x],main) ∀ (x,main). If
this returns true its just a trivial true signal, that is to expensive and
transzendental to get blocked.
>* I've changed AC_CHECK_LIB([m], [ceil]) to AC_CHECK_LIB([m], [main]) and it*
>* works. according to conftest.c, libtool generate a small peace of code to*
>* check whether the specific function exists or not. for AC_CHECK_LIB([m],*
>* [main]), the code is:*
>* main()*
>* {*
>* return main();*
>* ;*
>* return 0;*
>* }*
>* call main itself in gcc will cause a crash, why it can works here?*
>* *
>* *
>* On Thu, Jul 3, 2014 at 2:46 PM, Minxuan Zhuang <address@hidden> wrote:*
>* *
>*> hi：*
>*> I have a configure.ac file includes: AC_CHECK_LIB([m], [ceil])*
>*> then I got this result: checking for ceil in -lm... no*
>*> but a .c file contains ceil function works very well with or without -lm,*
>*> why is that?*
>*>*
>*> libtool version: 2.4.2*
>*> system： Ubuntu 13.04*
>*>*

**can't find ceil function in math library**, *Minxuan Zhuang*, `2014/07/03`
**Re: can't find ceil function in math library**, *Ingo Krabbe*, `2014/07/03`
**Re: can't find ceil function in math library**, *Minxuan Zhuang*, `2014/07/03`
**Re: can't find ceil function in math library**,
*Ingo Krabbe* **<=**

**Re: can't find ceil function in math library**, *ingo . krabbe*, `2014/07/03`
**Re: can't find ceil function in math library**, *ingo . krabbe*, `2014/07/03`
**Re: can't find ceil function in math library**, *ingo . krabbe*, `2014/07/03`