Strange compiler error

This is a discussion on Strange compiler error within the C Programming forums, part of the General Programming Boards category; When trying to compile a simple script with Gcc: Code: #include <stdio.h> #include <math.h> int main() { double a = ...

  1. #1
    Registered User
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    Strange compiler error

    When trying to compile a simple script with Gcc:
    Code:
    #include <stdio.h>
    #include <math.h>
    
    int main()
    {
    	double a = cos(360);
    	printf ("cos: %d\n\n", a);
    
    	double b = sin(360);
    	printf ("sin: %d\n\n", b);
    
    	double c = tan(45);
    	printf ("tan: %d\n\n", c);
    
    	return 0;
    }
    I get an error:

    /tmp/cckLVeVp.o: In function `main':
    trig.c.text+0x1b): undefined reference to `cos'
    trig.c.text+0x3f): undefined reference to `sin'
    trig.c.text+0x63): undefined reference to `tan'
    collect2: ld returned 1 exit status
    I compile via: gcc trig.c -o test, however when I compile using
    g++ trig.c -o test it works.

    Why is it compiling with c++ compiler and not c compiler since it is a c script ????

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    It seems you are failing to link with the C standard library. Consult the docs on how to do that.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  3. #3
    and the Hat of Guessing tabstop's Avatar
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    And of course Elysia means the math library, not the standard library. To link the math library, add -lm to the end of your gcc command line.

  4. #4
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by tabstop View Post
    And of course Elysia means the math library, not the standard library. To link the math library, add -lm to the end of your gcc command line.
    Duh, how am I supposed to know of a compiler that keeps two separate libraries?
    I'm living in the current and don't need to type commands from the command line to compile or link to whatever-you-call-it libraries. I push a simple button and it works. That is today.
    Hmph.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  5. #5
    Kernel hacker
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    Actually, what compiler needs what switches depends on both the compiler and the library implementation. The glibc that is used with Linux has a separate math library (which has the benefit that it can be replaced with a different math library, should someone wish to do so).

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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