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Undefined reference?!

Posted on 2006-05-08
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Last Modified: 2010-10-05
Hello,

I'm having trouble using the ceil() and floor() functions from the math.h library, when I compile a simple program I get this:
/tmp/ccbjF9bu.o(.text+0x5cc): In function `main':
: undefined reference to `ceil'
/tmp/ccbjF9bu.o(.text+0x5ee): In function `main':
: undefined reference to `floor'
collect2: ld returned 1 exit status

The code is:

float f = 2.5;

if( ceil(f)==f || floor(f)==f )
   printf("not decimal!");

It works fine if I pass them the value (ceil(2.5)) instead of the variable, though :S


Thanks in advance :)
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Question by:bass20
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Accepted Solution

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Kent Olsen earned 80 total points
ID: 16635638
Hi bass20,

The function prototype should, indeed, be in math.h.  But that doesn't necessarily ensure that they can be found for linking.  :(

Try adding "-lm" to the gcc command line.
 


Good Luck!
Kent
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LVL 53

Expert Comment

by:Infinity08
ID: 16637039
Or try this :

  ceil((double) f)

since you say ceil(2.5) works. Although it shouldn't make a difference.

Just a note though : comparing two floats (doubles) using the == will not always give the result you expect !
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Author Comment

by:bass20
ID: 16638333
The -lm option worked, thanks :)

Infinity: I didn't know that; in my case it worked, in what cases is it likely to fail?


Thanks :)
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LVL 53

Expert Comment

by:Infinity08
ID: 16638434
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