Issues with make and #include - c

Question

Somewhere between my headers and my Makefile I'm not doing the dependencies correctly, and it's not compiling. This really only has anything to do with the first few lines from each code, but I posted all the code for reference
I'm trying to split up a who clone into 3 parts. Here is the original for reference. The exercise is to make it with utmp, so you also need utmplib
So I've split it up into 3 files, the first one being show.h
#include <stdio.h>
#include <sys/types.h>
#include <utmp.h>
#include <fcntl.h>
#include <time.h>
#include <stdlib.h>
#define SHOWHOST
void show_info(struct utmp *);
void showtime(time_t);
then I have show.c
/*
* * show info()
* * displays the contents of the utmp struct
* * in human readable form
* * * displays nothing if record has no user name
* */
void show_info( struct utmp *utbufp )
{
if ( utbufp->ut_type != USER_PROCESS )
return;
printf("%-8.8s", utbufp->ut_name); /* the logname */
printf(" "); /* a space */
printf("%-8.8s", utbufp->ut_line); /* the tty */
printf(" "); /* a space */
showtime( utbufp->ut_time ); /* display time */
#ifdef SHOWHOST
if ( utbufp->ut_host[0] != '\0' )
printf(" (%s)", utbufp->ut_host); /* the host */
#endif
printf("\n"); /* newline */
}
void showtime( time_t timeval )
/*
* * displays time in a format fit for human consumption
* * uses ctime to build a string then picks parts out of it
* * Note: %12.12s prints a string 12 chars wide and LIMITS
* * it to 12chars.
* */
{
char *ctime(); /* convert long to ascii */
char *cp; /* to hold address of time */
cp = ctime( &timeval ); /* convert time to string */
/* string looks like */
/* Mon Feb 4 00:46:40 EST 1991 */
/* 0123456789012345. */
printf("%12.12s", cp+4 ); /* pick 12 chars from pos 4 */
}
and finally, `who3.c'
/* who3.c - who with buffered reads
* - surpresses empty records
* - formats time nicely
* - buffers input (using utmplib)
*/
#include "show.h"
int main()
{
struct utmp *utbufp, /* holds pointer to next rec */
*utmp_next(); /* returns pointer to next */
if ( utmp_open( UTMP_FILE ) == -1 ){
perror(UTMP_FILE);
exit(1);
}
while ( ( utbufp = utmp_next() ) != ((struct utmp *) NULL) )
show_info( utbufp );
utmp_close( );
return 0;
}
So I created my Makefile:
who3:who3.o utmplib.o
gcc -o who who3.o utmplib.o
who3.o:who3.c show.c
gcc -c who3.c show.o
show.o:show.c
gcc -c show.c show.h
utmplib.o:utmplib.c
gcc -c utmplib.c
clean:
rm -f *.o
Unfortunately there's an error when I do make:
gcc -o who who3.o utmplib.o
who3.o: In function `main':
who3.c:(.text+0x38): undefined reference to `show_info'
collect2: error: ld returned 1 exit status
make: *** [who3] Error 1
As I said earlier, I haven't done my dependencies correctly, and I'm not sure what I did wrong. How do I do my dependencies correctly?

Answer 1

It looks like you are missing show.o from the dependencies and from the list of object files of the command for building who3 in your makefile.
Also, the command for who3.o looks wrong. You are compiling only -c, but you are passing an object file as input (show.o). You should remove show.o from the rule and show.c doesn't belong on the list of dependencies of who3.o either.
Also, the command for show.o looks wrong. You shouldn't be passing header files (show.h) to the compiler; they only need to be referenced as #include in the source files.
Also, you are inconsistent about what your default is actually called. You say it is who3 in the rule (who3: ...) but the command will actually build a task called who (gcc -o who ...).