Undefined symbol in gcc & c++

From: Stanley Yao (yao_at_CS.Arizona.EDU)
Date: 07/22/03 

Date: Tue, 22 Jul 2003 09:56:57 -0700

Dear All,

I built the following little C program into a library (libtt.a) with gcc:

/* Filename: tt1.c */
#include <stdio.h>
int foo() {
    return 1;
}

gcc -c tt1.c
ar -rs libtt.a tt1.o

Then I wrote the following C++ program and want to link with libtt.a and
failed.

/* Filename: tt2.cc */
int foo();
int main() {
  int k;
  k = foo();
  return 0;
}

% c++ tt2.cc -L. -ltt
Undefined first referenced
 symbol in file
foo() /var/tmp//cc02ILOd.o
ld: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status

% c++ tt2.cc tt1.o
Undefined first referenced
 symbol in file
foo() /var/tmp//ccgMpZee.o
ld: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status

% g++ tt2.cc libtt.a
Undefined first referenced
 symbol in file
foo() /var/tmp//cc8Kx1jd.o
ld: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status

% gcc tt2.cc tt1.o
Undefined first referenced
 symbol in file
foo() /var/tmp//ccUM2g0c.o
__gxx_personality_v0 /var/tmp//ccUM2g0c.o
ld: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status

Did I do something wrong? How can I get these 2 pieces (one is C, the
other is C++) linked together?

Thank you very much!
-Stan