Programming

#include <stdio.h>

extern void func(void);

int
main(int argc, char **argv)
{
    printf("Before func\n");
    func();
    return 0;
}

#include <stdio.h>

void
func(void)
{
    printf("In func\n");
}

gcc -c func.c
gcc -c main.c
ar rc func.a func.o
gcc -o test main.o func.a

ld: warning: ignoring file func.a, file was built for archive which is not the architecture being linked (x86_64): func.a
Undefined symbols for architecture x86_64:
  "_func", referenced from:
      _main in main.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status

Before func
In func

ar -tv func.a

rw-r--r--     501/20           24 Dec 12 21:41 2014 __.SYMDEF SORTED
rw-r--r--     501/20          816 Dec 12 21:41 2014 func.o

ar -s func.a

rw-r--r-- 502/20    684 Dec 12 20:29 2014 func.o

ld: warning: ignoring file func.a, file was built for archive which is not the architecture being linked (x86_64): func.a
Undefined symbols for architecture x86_64:
  "_func", referenced from:
      _main in main.o

/usr/bin/gcc -c func.c main.c
/usr/bin/ar -src func.a func.o
/usr/bin/gcc -o test main.o func.a

func.o: Mach-O 64-bit object x86_64
main.o: Mach-O 64-bit object x86_64