undefined reference to function called 'full_adder(BIT A, BIT B, BIT Ci, BIT *Co)'

Question

I am a CS student learning how to program in C. I have 3 files and a Makefile. I have

logic.c logic.h main.c

the top of logic.c is:

 #include "logic.h" 
//use this function in 4 bit adder 
//BIT full_adder(BIT A, BIT B, BIT Ci, BIT *Co);
int adder(int O1, int O2,  BIT carryIn, BIT *carryOut){
printf("in adder");
return 0x0;
}


BIT full_adder(BIT A, BIT B, BIT Ci, BIT *Co){ 
BIT S = FALSE; 
    //implementation of if else's based on Truth Table <br>
    if((A==FALSE)&&(B==FALSE)&&(Ci==FALSE)){ 
        S=FALSE; 
        *Co = FALSE; 
    } <br>
    return S; 
}

the top of main.c is:

 #include "logic.h"
BIT full_adder(BIT A, BIT B, BIT Ci, BIT *Co);

in main.c I have my main function, at the bottom of main function I have :

 assert((full_adder(FALSE,FALSE,FALSE,&Co)==FALSE) && (Co==FALSE));
        adder(FALSE,FALSE,FALSE,&Co2);   
    return 0;

I am getting the error:

 main.o: In function 'main': main.c:158: undefined referenceto 'full_adder' 

collect2: ld returned 1 exit status <br>
make: *** [pa3] Error 1 <br>
./bscript: line 3: pa3: command not found

This is homework, but I have spent a good deal of time on this problem and am looking for some help. I have the correct return type for adder, full_adder, and I declare the function in the top of both logic.c and main.c.

The questions that did not answer my question were:

Any help is appreciated.

EDIT: logic.c is getting compiled and it does create a logic.o file.

EDIT: my prof says that I cannot edit logic.h

EDIT: makefile:

# Makefile template for CS 270 (specialized for PA3) 

# List of files
C_SRCS      = main.c logic.c
C_OBJS      = main.o logic.o
C_HEADERS   = logic.h
OBJS        = ${C_OBJS} 
EXE         = pa3 

# Compiler and loader commands and flags
GCC         = gcc
GCC_FLAGS   = -g -std=c99 -Wall -O0 -c
LD_FLAGS    = -g -std=c99 -Wall -O0
# Target is the executable
pa3 : $(OBJS)
    @echo "Linking all object modules ..."
    $(GCC) $(LD_FLAGS) $(OBJS) -o $(EXE)
    @echo ""
# Recompile C objects if headers change
${C_OBJS}:      ${C_HEADERS}
# Compile .c files to .o files
.c.o:
    @echo "Compiling each C source file separately ..."
    $(GCC) $(GCC_FLAGS) $<
    @echo ""

# Clean up the directory
clean:
    @echo "Cleaning up project directory ..."
    rm -f *.o $(EXE) core a.out
    @echo ""

EDIT: I compile my code with the script:

#!/usr/bin/sh
make
pa3

@H2CO3 I think you mean 'am I making a logical representation of a full adder?' Yes. Many not gates and and gates and ultimately I will be making a 4 bit adder. — Clara, Sep 20 '12 at 16:12
At least my answer makes no changes to the `logic.h` file. I just included a trimmed down version of it to show where things should go, nothing more. Have you tried the suggested change to `logic.c` and `main.c`? — HonkyTonk, Sep 21 '12 at 11:39

HonkyTonk · Accepted Answer · 2012-09-20T15:57:00.997

First of all, separate definitions from declarations:

logic.h:

#ifndef _LOGIC_H_
#define _LOGIC_H_

/* Define BIT as before */

int adder(int O1, int O2,  BIT carryIn, BIT *carryOut);
BIT full_adder(BIT A, BIT B, BIT Ci, BIT *Co);


#endif

logic.c:

#include <stdio.h>
#include "logic.h"

int adder(int O1, int O2,  BIT carryIn, BIT *carryOut){
  printf("in adder");
  return 0x0;
}

BIT full_adder(BIT A, BIT B, BIT Ci, BIT *Co){
  BIT S = FALSE;
  //implementation of if else's based on Truth Table
  if((A==FALSE)&&(B==FALSE)&&(Ci==FALSE)){
    S=FALSE;
    *Co = FALSE;
  }

  return S;
}

main.c:

#include "logic.h"

int main(int argc, char* argv[]) {
  /* Do your stuff */
  return 0;
}

Now things are where they should be and your logic.h supplies the needed information to the compiler.

Your makefile should not need any fancy stuff with only these three files.

This needs to be done via the makefile:

gcc -c -o main.o main.c
gcc -c -o logic.o logic.c
gcc -o main main.o logic.o

(The logical problems that you have in your full_adder are left for your to solve...)

Scooter · Answer 2 · 2012-09-20T23:06:11.000

I have seen linkers not-find/find functions depending on the order of the object files. In your makefile you may want to try changing the order:

C_OBJS      = logic.o main.o

I declare the function in the top of both logic.c and main.c.

The function prototype

BIT full_adder(BIT A, BIT B, BIT Ci, BIT *Co);

should only occur once, in logic.h.

The error you are getting is from the linker.

You may want to just try and compile/link it outside the Makefile:

gcc -c logic.c
gcc -o main main.c logic.o

undefined reference to function called 'full_adder(BIT A, BIT B, BIT Ci, BIT *Co)'

2 Answers2