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Static Library Linker Error {Dev C++ / GCC}

This is a discussion on Static Library Linker Error {Dev C++ / GCC} within the C Programming forums, part of the General Programming Boards category; Hey everyone. I'm trying to create & use a static library but kind of stuck at something I can't quite ...

  1. #1
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    Question Static Library Linker Error {Dev C++ / GCC}

    Hey everyone.
    I'm trying to create & use a static library but kind of stuck at something I can't quite grasp...

    I have created library file containing just 2 functions dealing with temperature conversion. I typed the source(.c) file and the headre(.h) file & compiled them to get the library(.a) file.

    Now when i use it in a new program I get a LINKER ERROR at the call to the function defined in the library.
    [Linker error] undefined reference to `toFahrenheit'
    ld returned 1 exit status


    I'm not sure where I made the mistake... while writing the source or I'm missing something about linking?

    I'm posting my codes.

    Source File fore creating the library "temperature.c"
    Code:
    /*
    temperature library file
    */
    
    double c,f,k;
    
    double toCelsius(double x)
    {
           c = (x-32)*5/9;
           return c;
    }
    
    double toFahrenheit(double x)
    {
           f = x*5/9+32;
           return f;
    }
    Header file "temperature.h"
    Code:
    /*
    header file : temperature
    */
    extern double toCelsius(double);
    extern double toFahrenheit(double);
    New Program "Test.c"
    Code:
    //testing temperature library
    #include<stdio.h>
    #include "temperature.h"
    
    int main()
    {
        double c,f;
        printf("enter Celsius\t");
        scanf("%f",&c);
        f = toFahrenheit(c);
        printf("Fahrenheit = %d",f);
        
        int ch;
        while((ch = getchar()) != '\n' && ch != EOF);
        return 0;
    }


    P.S.
    I'm using Dev C++ v4.9.9.2
    with GCC v3.4.2 on Windows 7

  2. #2
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    This indicates that when you compiled the user binary (that uses your library) you did not include the library object. Not sure how you would do this in Dev-C++ but with GCC on the command line it would be like this:

    gcc -o program object.a userfile.c

    instead of
    gcc -o program userfile.c

  3. #3
    and the hat of wrongness Salem's Avatar
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    In something like project->settings->source files, you need to make sure "temperature.c" is also listed as a source file, along with Test.c

    You should be able to see the project "tree" on the left of the IDE.
    stahta01 likes this.
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    Hey, Tanu.

    I would make sure that you have added all source files to your current project if you are using Dev. I'm not sure what you mean by "with GCC", I didn't know you could get GCC functionality in Dev.
    Anyway if you make sure you have all source files in a project together, that should fix the problem.

    I'd also try using #include "temperature.h" in at the top of your file temperature.c . Can anyone else verify this is necessary? I always use this in all non .h files that are coordinated by one .h, and it's always worked. I haven't tried leaving it out.

  5. #5
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    Quote Originally Posted by Derek Lake View Post
    Hey, Tanu.

    I would make sure that you have added all source files to your current project if you are using Dev. I'm not sure what you mean by "with GCC", I didn't know you could get GCC functionality in Dev.
    Anyway if you make sure you have all source files in a project together, that should fix the problem.

    I'd also try using #include "temperature.h" in at the top of your file temperature.c . Can anyone else verify this is necessary? I always use this in all non .h files that are coordinated by one .h, and it's always worked. I haven't tried leaving it out.
    1. He is using #include "temperature.h", if he wasn't the error would be different (something like implicit declaration of function X)
    2. Undefined reference is at the LINKER stage, not the compilation stage. This has nothing to do with includes, it means the linker literally can't find the library that the referenced function belongs to.
    3. Yes its necessary if you are calling functions that are prototyped/declared in the header file you are including.

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