c++ "undefined reference"

kpachopoulos · 01-15-2007, 12:08 PM

Hi,
i am new to C++. Attempting to compile my code, i get the following output. Could somebody help me out with this "undefined reference" error?

Code:

kostas@home:~/programming/c++$ g++ ctest3.cc
In file included from /usr/lib/gcc/x86_64-linux-gnu/4.1.2/../../../../include/c++/4.1.2/backward/fstream.h:31,
                 from ctest3.cc:2:
/usr/lib/gcc/x86_64-linux-gnu/4.1.2/../../../../include/c++/4.1.2/backward/backward_warning.h:32:2: warning: #warning This file includes at least one deprecated or antiquated header. Please consider using one of the 32 headers found in section 17.4.1.2 of the C++ standard. Examples include substituting the <X> header for the <X.h> header for C++ includes, or <iostream> instead of the deprecated header <iostream.h>. To disable this warning use -Wno-deprecated.
ctest3.cc:48:2: warning: no newline at end of file
/tmp/cc8HjuEt.o: In function `main':
ctest3.cc:(.text+0x7a): undefined reference to `bit_file_c::bit_file_c()'
ctest3.cc:(.text+0x8d): undefined reference to `bit_file_c::Open(char const*, BF_MODES)'
ctest3.cc:(.text+0x15b): undefined reference to `bit_file_c::GetBit()'
ctest3.cc:(.text+0x189): undefined reference to `bit_file_c::Close()'
ctest3.cc:(.text+0x1e3): undefined reference to `bit_file_c::~bit_file_c()'
ctest3.cc:(.text+0x1f9): undefined reference to `bit_file_c::~bit_file_c()'
collect2: ld returned 1 exit status

The program uses a bit manipulation/editing library, i have found in http://michael.dipperstein.com/bitlibs/#bitfile_cpp
Both the .cpp and .h files have been placed in the same directory, as my source (.cc) file. Heres' my code:

Code:

#include "bitfile.h"
#include <fstream.h>
#include <sys/stat.h>
#include <iostream.h>
#include <string.h>

#define EXIT_FAILURE 1

using std::string;
using namespace std;


int main()
{
	bit_file_c bf;
	int i, value;
	
	try
	{
		bf.Open("/home/kostas/lzw/dict.txt", BF_READ);
	}
	catch (const char *errorMsg)
	{
		cout << errorMsg << endl;
		return (EXIT_FAILURE);
	}
	catch (...)
	{
		cout << "Unknown error opening file" << endl;
		return (EXIT_FAILURE);
	}	


	for (i = 0; i < 100; i++)
	{
		value = bf.GetBit();
		if(value == EOF)
		{
			cerr << "error: reading bit" << endl;
			bf.Close();
			return (EXIT_FAILURE);
		}
		else
		{
			cout << "read bit " << value << endl;
		}
	}
}

taylor_venable · 01-15-2007, 12:45 PM

You're getting a linker error. Try either: (1) compiling all the source files together with one call to the compiler, or (2) compile each source file to object files, then compile all the object files together.

(1) g++ -g -Wall ctest3.cc bitfile.cpp
(2) g++ -g -Wall -c ctest3.cc; g++ -g -Wall -c bitfile.cpp; g++ -g *.o

I believe those commands should set you right.

matthewg42 · 01-15-2007, 01:07 PM

The error "undefined reference to ..." means the linker can't find the object code for some symbol which is used in your program, in this case the implementation of bit_file_c::bit_file_c() and others mentioned in the error message.

I downloded the bitfile code from the page you linked to. Did you build it yet (using the make command)? If so, you should have a file called bitfile.o. This is the object file containing the necessary object code. All you have to do is tell the compiler to look in this file:

Code:

g++ ctest3.cc bitfile.o -o ctest3

Other minor things: The C++ header files should not have the .h suffix. Since the C++ standard was made, youo should be including headers like this (note some old C headers still use the .h suffix) :

Code:

#include "bitfile.h"
#include <sys/stat.h>
#include <fstream>
#include <iostream>
#include <string>

It generally works with the .h, but the namespaces will probably not be set up properly.

One last thing, I personally prefer to call all C++ files .cpp rather then .cc. This seems to be the norm these days.