What am I doing wrong?, linking in C++

Question

I'm trying to code a simple base64 encoder/decoder (to test my programming skill).

I can compile it, but it doesn't link, I've this message error:

C:\Documents and Settings\Facon\Escritorio>g++ base64.o main.o -o prueba.exe

main.o:main.cpp:(.text+0x24a): undefined reference to `Base64Encode(std::vector > const&)'

collect2: ld returned 1 exit status

Compiler & Linker: Mingw32 3.4.5 SO: Windows XP

This is my source code:

base64.h:

#ifndef BASE64_H
#define BASE64_H

#include <iostream>
#include <vector>

typedef unsigned char byte;

std::string Base64Encode(const std::vector<byte> &array);
std::vector<byte> Base64Decode(const std::string &array);

#endif

base64.cpp:

#include "base64.h"

std::string Base64Encode(std::vector<byte> &array)
{
 const char *base64_table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
 const unsigned int size = array.size();
 std::string output;

 for (unsigned int i = 0; (i < size); i++)
 {
  if ((size - i) > 3)
  { 
   output.push_back(static_cast<char>(base64_table[array[i] >> 2]));
   output.push_back(static_cast<char>(base64_table[((array[i++] & 0x03) << 4) | ((array[i] & 0xF0) >> 4)]));
   output.push_back(static_cast<char>(base64_table[((array[i++] & 0x0F) << 2) | ((array[i] & 0xC0) >> 4)]));
   output.push_back(static_cast<char>(base64_table[array[i] & 0x3F]));
  }
  else if ((size - i) == 3)
  {
   output.push_back(static_cast<char>(base64_table[array[i] >> 2]));
   output.push_back(static_cast<char>(base64_table[((array[i++] & 0x03) << 4) | ((array[i] & 0xF0) >> 4)]));
   output.push_back(static_cast<char>(base64_table[(array[i] & 0x0F) << 2]));
   output.push_back(static_cast<char>('='));
  }
  else if ((size - i) == 2)
  {
   output.push_back(static_cast<char>(base64_table[array[i] >> 2]));
   output.push_back(static_cast<char>(base64_table[(array[i] & 0x03) << 4]));
   output.push_back('=');
   output.push_back('=');
  }
 }

 return output;
}

std::vector<byte> Base64Decode(const std::string &array) // TODO
{
 const char *base64_table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
}

main.cpp:

#include <iostream>
#include <vector>
#include "base64.h"

using namespace std;

int main(int argc, char *argv[])
{
 const char* prueba = "sure.";
 vector<byte> texto;
 string codificado;

 for (unsigned int i = 0; (prueba[i] != 0); i++)
 {
  texto.push_back(prueba[i]);
 }

 codificado = Base64Encode(texto);

 cout << codificado;

 return 0;
}

PD: Sorry for my bad knowledge of English :P

Check your posted code snippets, you should have gotten a compile error, not a link error. — Hans Passant

Motti Motti · Accepted Answer · 2010-04-18T14:15:36

You're missing a const in the implementation of Base64Encode, it's declared as:

std::string Base64Encode(const std::vector<byte> &array);

But implemented as

std::string Base64Encode(std::vector<byte> &array) { ... }

The compiler thinks that you've overloaded the function (for const and non-const vectors) and thinks the implementation of the const version is missing.

What am I doing wrong?, linking in C++

3 Answers