How to link multiple .c files - c

Question

I know that you have to create a header file and #include it in your main. I have done that and when I compile my code for some reason it is unable to figure out where one of my functions are.
The layout of my project is a: threads.c makeCityFromInput.h and makeCityFromInput.c
I have the threads.c #including the makeCityFromInput.h
This is what happens when I try to compile:
make
gcc -ggdb -std=c99 -Wall -Wextra -pthread -c threads.c
gcc -ggdb -std=c99 -Wall -Wextra -pthread -o threads threads.o -lm -lncursesw -pthread
threads.o: In function `main':
/home/project3/threads.c:183: undefined reference to `readConfig'
collect2: error: ld returned 1 exit status
Makefile:71: recipe for target 'threads' failed
make: *** [threads] Error 1
It is unable to find my readconfig file even though it is in my header file
my threads.c file
#define _DEFAULT_SOURCE
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <strings.h>
#include <string.h>
#include <ncurses.h> //displays the cars
#include <pthread.h> //threading
#include <unistd.h>
#include "makeCityFromInput.h"
#define MAX 2048
int main(int argc, char *argv[]){
//Expected input: Name of config file
// If the config file is not given; or too many config files are given
if (argc != 2){
endwin();
fprintf(stderr, "Usage: Enter a configuration file");
exit( EXIT_FAILURE );
}
FILE *fp = NULL;
fp = fopen(argv[1], "r");
assert( fp );
readConfig(fp);
fclose( fp );
return 0;
}
my makeCityFromInput.h file:
#ifndef _MAKECITYFROMINPUT_H
#define _MAKECITYFROMINPUT_H
void readConfig(FILE *fp);
int *parse_line(char *line, int *numInts);
void create_skyline(int *ground, int size, int maxMissiles);
#endif
my makeCityFromInput.c file:
#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <strings.h>
#include <string.h>
#include <ncurses.h> //displays the cars
#include <pthread.h> //threading
#include <unistd.h>
void readConfig(FILE *fp){
...
}
My make file
#
# Created by gmakemake (Ubuntu Jul 25 2014) on Wed Nov 14 20:05:05 2018
#
#
# Definitions
#
.SUFFIXES:
.SUFFIXES: .a .o .c .C .cpp .s .S
.c.o:
$(COMPILE.c) $<
.C.o:
$(COMPILE.cc) $<
.cpp.o:
$(COMPILE.cc) $<
.S.s:
$(CPP) -o $*.s $<
.s.o:
$(COMPILE.cc) $<
.c.a:
$(COMPILE.c) -o $% $<
$(AR) $(ARFLAGS) $# $%
$(RM) $%
.C.a:
$(COMPILE.cc) -o $% $<
$(AR) $(ARFLAGS) $# $%
$(RM) $%
.cpp.a:
$(COMPILE.cc) -o $% $<
$(AR) $(ARFLAGS) $# $%
$(RM) $%
CC = gcc
CXX = g++
RM = rm -f
AR = ar
LINK.c = $(CC) $(CFLAGS) $(CPPFLAGS) $(LDFLAGS)
LINK.cc = $(CXX) $(CXXFLAGS) $(CPPFLAGS) $(LDFLAGS)
COMPILE.c = $(CC) $(CFLAGS) $(CPPFLAGS) -c
COMPILE.cc = $(CXX) $(CXXFLAGS) $(CPPFLAGS) -c
CPP = $(CPP) $(CPPFLAGS)
########## Flags from header.mak
CFLAGS = -ggdb -Wall -Wextra -pedantic -std=c99 -pthread
# program uses pthreads and curses libraries
CLIBFLAGS = -lncursesw -lpthread -lrt
########## End of flags from header.mak
CPP_FILES =
C_FILES = pt-cruisers.c racer.c
PS_FILES =
S_FILES =
H_FILES = racer.h
SOURCEFILES = $(H_FILES) $(CPP_FILES) $(C_FILES) $(S_FILES)
.PRECIOUS: $(SOURCEFILES)
OBJFILES = racer.o
#
# Main targets
#
all: pt-cruisers
pt-cruisers: pt-cruisers.o $(OBJFILES)
$(CC) $(CFLAGS) -o pt-cruisers pt-cruisers.o $(OBJFILES) $(CLIBFLAGS)
#
# Dependencies
#
pt-cruisers.o: racer.h
racer.o: racer.h
#
# Housekeeping
#
Archive: archive.tgz
archive.tgz: $(SOURCEFILES) Makefile
tar cf - $(SOURCEFILES) Makefile | gzip > archive.tgz
clean:
-/bin/rm -f $(OBJFILES) pt-cruisers.o core
realclean: clean
-/bin/rm -f pt-cruisers

Answer 1

It looks like this
gcc -ggdb -std=c99 -Wall -Wextra -pthread -c threads.c
gcc -ggdb -std=c99 -Wall -Wextra -pthread -c makeCityFromInput.c
gcc -ggdb -std=c99 -Wall -Wextra -pthread -o threads threads.o makeCityFromInput.o -lm -lncursesw -pthread
If you show your make file we can also help with that...

Answer 2

I guess what you are actually asking is "What is wrong with my makefile?". As you have not provided it I can only take an educated guess. Here is a GNUmake snippet to build your program:
.PHONY: default
default: threads
CC := ...
LD := ...
CFLAGS := ...
LDFLAGS := ...
LIBS := ...
SRCS := threads.c makeCityFromInput.c
OBJS := $(SRCS:%.c=%.o)
$(OBJS): %.o: %.c
$(CC) $(CFLAGS) -o $# -c $<
threads: $(OBJS)
$(LD) $(LDFLAGS) -o $# $^ $(LIBS)