undefined reference to 'sqrt'

This is a discussion on undefined reference to 'sqrt' within the C Programming forums, part of the General Programming Boards category; Help! Where is the mistake ? Code: double x = 0.0 , y = 0.0, r = x*x + y*y; ...

  1. #1
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    Angry undefined reference to 'sqrt'

    Help! Where is the mistake ?
    Code:
    double x = 0.0 , y = 0.0, r = x*x + y*y;
    ...
    printf("\n%i	%.2f	%.2f	%.2f\n",i,x,y,sqrt(r));
    ...ore sqrt(x*x + y*y));
    The compiler tell me things like this:
    gmake[2]: *** [c_teilchen_in_kasten] Fehler 1
    gmake[2]: Das Target »all« wurde wegen Fehlern nicht aktualisiert.
    /home/joerg/c_teilchen_in_kasten/src/c_teilchen_in_kasten.c:82: undefined reference to `sqrt'

    Thanks for life out there !

  2. #2
    ZuK
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    you have to link to the math library.
    add -lm to the linker flags.
    Kurt

  3. #3
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    #include <stdio.h>
    #include <stdlib.h>
    #include <math.h>
    #define N 5

    I did !

  4. #4
    ZuK
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    No. That's just including the math header.
    I don't know what gmake is or what kind of ide you're using. this -lm flag has to be added either to your projects linker options or to your projects makefile.
    Kurt

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    I'm using Kdevelop under suse linux 10.2

  6. #6
    ZuK
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    Quote Originally Posted by joerg View Post
    I'm using Kdevelop under suse linux 10.2
    Guess you have to wait some time. Have just started to install kdevelop. Maybe sombody else can help in the meantime.
    Kurt

  7. #7
    ZuK
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    Sorry but it will take a few month until I understand kdevelops project management.
    you could try to compile from the commandline in the meantime
    e.g.
    Code:
    gcc c_teilchen_in_kasten.c -lm
    Kurt

  8. #8
    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
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    Quote Originally Posted by joerg View Post
    I'm using Kdevelop under suse linux 10.2
    So? You'll have to tell kdev that you WANT the math lib (-lm).

  9. #9
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    Thank you Kurt !

    It's a mess.
    you wright a couple of words for source code, therefore you have to go through a jungle of s...
    and Kdelvelop creates an entire PROJEKT !

    Joerg

  10. #10
    and the hat of wrongness Salem's Avatar
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    For simple projects, certainly those in a single file, compiling from the command line is easiest.
    Plus you get to learn about all the things like include and library paths etc.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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