Compiling problem

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  1. #1
    & the hat of GPL slaying Thantos's Avatar
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    Compiling problem

    Trying to compile some code on my debian machine and am getting an error. I have to trouble getting it to compile on my XP machine. Compiler is gcc on both machines.

    Error is:
    Code:
    /tmp/ccFbD8lA.o: In function `main':  
    /tmp/ccFbD8lA.o(.text+0x9d): undefined reference to `sqrt'
    collect2: ld returned 1 exit status
    Code is:
    Code:
    #include <stdio.h>
    #include <math.h>
    
    int main()
    {
            int a, b, c, a2;
            float x1, x2, part1;
    
    
            printf("A: ");
            scanf("%d", &a);
            printf("B: ");
            scanf("%d", &b);
            printf("C: ");
            scanf("%d", &c);
    
            part1 = sqrt( (b*b) - 4*a*c);
            a2 = 2*a;
            printf("-b = %d\nB^2 - 4AC = %f\n2A = %d.\n", -b, part1, a2);
    
            x1 = ((-b) + part1) / (2*a);
            x2 = ((-b) - part1) / (2*a);
    
            printf("X = %f\nX = %f", x1, x2);
            return 0;
    }

  2. #2
    and the hat of wrongness Salem's Avatar
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    gcc prog.c -lm

    That's lowercase LM
    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.

  3. #3
    & the hat of GPL slaying Thantos's Avatar
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    Ok it worked but what does the -lm do? I searched the man page for it and didn't even see that switch listed. Also it outputed the exe as a.out instead of prog.exe. Anyway to change this?

    BTW not used to command line compilers so bear with me please

  4. #4
    and the hat of wrongness Salem's Avatar
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    The 'l' specifies that you want to include additional libraries (usually found in /usr/lib)

    The parameter -lxxx
    means you want to link a library called libxxx.a
    That is, the lib prefix and .a suffix are assumed.

    It's a feature of history that libm is separate from libc

    The companion -L option specifies where to look for libraries, in case you have your own.

    > Also it outputed the exe as a.out instead of prog.exe.
    gcc -o prog.exe prog.c -lm

    a.out, short for assember.out, being the traditional default name for the final result of compiling and linking a program.
    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.

  5. #5
    & the hat of GPL slaying Thantos's Avatar
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    Thanks Salem. I understand now.

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