Undefined Reference Error

This is a discussion on Undefined Reference Error within the C Programming forums, part of the General Programming Boards category; I am getting an Undefined reference to <function>, here is my code: Code: #include <stdio.h> #include "qsolver.h" int main() { ...

  1. #1
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    Undefined Reference Error

    I am getting an Undefined reference to <function>, here is my code:

    Code:
    #include <stdio.h>
    #include "qsolver.h"
    
    
    int main() {
    	double a, b, c, x1, x2;
    	int qret;
    
    	while(1) {
    		printf("Enter variables for quadratic equation (type: \n");
    		scanf("%lf %lf %lf", &a, &b, &c);
    
    		if((qret = qsolver(a, b, c, &x1, &x2)) != 0) {
    			printf("Error Value:  %d\n", qret);
    		}
    	}
    	return 0;
    }
    
    ******************************************************************************
    
    #include <stdio.h>
    #include <math.h>
    #include "qsolver.h"
    
    int qsolver(double a, double b, double c, double* x1, double* x2) {
    
    	//Is the user giving an input which would divide by zero?
    	if(a == 0) {
    		printf("Input Not A Quadratic; Cannot Have Value Of '0' For A\n");
    		return 1;
    	}
    
    	//Is the user giving and input which would try to compute a square root of a negative number.
    	else if( (4*a*c) > pow(b,2) ) {
    		printf("There Are No Real Solutions; B^2 Is Less Than (4*A*C)\n");
    		return 2;
    	}
    
    	//The user input is valid, solve accordingly
    	else {
    		*x1 = (-b + sqrt(pow(b,2) - (4*a*c)))/(2*a);
    		*x2 = (-b - sqrt(pow(b,2) - (4*a*c)))/(2*a);
    		
    		return 0;
    	}
    }
    
    *****************************************************************************************
    
    #ifndef QSOLVER_H
    #define QSOLVER_H
    
    int qsolver(double, double, double, double *, double *);
    
    #endif

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    You'll have to compile all your .c files and link them together. (Most people don't actually run the linker separately; usually your compiler will do it for you, but you have to compile your .c files together.)

  3. #3
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    I have a Makefile I am using to link the files together but I am still getting the error. If you would like I can post that also

  4. #4
    and the Hat of Guessing tabstop's Avatar
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    Well, that wouldn't hurt.

  5. #5
    Captain Crash brewbuck's Avatar
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    Instead of <function> why not tell us which function it actually is? I suspect you're not linking with the math library.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  6. #6
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    The function is qsolver; here is the code to the makefile also which I believe links the math library:

    Code:
    CC = gcc
    CFLAGS= -Wall -pedantic
    
    q:  q.o q.solver.o
    	${CC} -o q q.o qsolver.o -lm
    q.o:  q.s
    	${CC} -c q.s
    qsolver.o:  qsolver.s
    	${CC} -c qsolver.s
    q.s:  q.c qsolver.h
    	${CC} ${CFLAGS} -s q.c
    qsolver.s:  qsolver.c qsolver.h
    	${CC} ${CFLAGS} -s qsolver.c
    clean:
    	rm -f *.o *.s q core

  7. #7
    a_capitalist_story
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    Code:
    q:  q.o q.solver.o
    Shouldn't q.solver.o be qsolver.o?

  8. #8
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by NuNn View Post
    The function is qsolver; here is the code to the makefile also which I believe links the math library:
    Well, I think your problem is in your makefile. Why are you compiling to ASSEMBLY first? Also, you say that "q" depends on something called "q.solver.o", yet you link with qsolver.o -- that means that qsolver.o will not get rebuilt because it's not listed as a dependency.

    Surely your linker is also printing some error like "Can't find qsolver.o"

    Try this:

    Code:
    CC = gcc
    CFLAGS= -Wall -pedantic
    
    q:  q.o qsolver.o
    	$(CC) -o $@ $^ -lm
    
    q.o:  q.c
    
    qsolver.o:  qsolver.c
    
    clean:
    	rm -f *.o q core
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  9. #9
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    Yep, typo on my part with the q.solver.o

    brewbuck: Thank you that fixed the problem. Could you tell me what the "$@ $^" symbols mean?
    Last edited by NuNn; 01-15-2009 at 12:01 PM.

  10. #10
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by NuNn View Post
    Yep, typo on my part but the "undefined reference" still remains
    So you admit the makefile you posted is not the actual makefile. I don't want to waste my time speculating when you won't show the real stuff.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  11. #11
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    Brewbuck what are you talking about????? That was my actual makefile. No need to get offensive here. I was thanking you for fixing my problem.............

  12. #12
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by NuNn View Post
    Brewbuck what are you talking about????? That was my actual makefile. No need to get offensive here. I was thanking you for fixing my problem.............
    I misunderstood you. I thought you meant you made a typo while retyping the makefile to post to the forum, and I hate it when people retype instead of copy-pasting. Sorry.

    The special variable $@ means "the target", i.e. the thing on the left side of the colon. The variable $^ means "the dependencies," i.e. everything to the right of the colon. It makes maintenance of your makefile easier, because when you add a dependency you don't have to update the rule.

    There are other specials, like $? which means "only the dependencies which have actually changed."
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  13. #13
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    Alrighty, thank you very much for your help. Otherwise I would have been sitting thinking for a while trying to figure it out haha.

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