Question

It seems like my two files, userinterface.h

#ifndef USERINTERFACE_H
#define USERINTERFACE_H

#include <string>
#include "vocabcollection.h"

namespace user_interface
{
//Finds a file
//
//Returns when user selects a file
std::string findFile();

//more comments followed by functions
}

#endif

and userinterface.cpp,

#include "userinterface.h"
using namespace std;
using namespace user_interface;

string findFile()
{
    return "./";
}

//more placeholder implementations of such functions; void functions have nothing within
//the brackets

are giving me this slew of errors from the linker:

Undefined symbols for architecture x86_64:
make: Leaving directory `longdirectorypath'
  "user_interface::showTestResults(int, int)", referenced from:
      vocabCollection::test()      in vocabcollection.o
  "user_interface::get(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)", referenced from:
      addNewCollection()     in mainlogic.o
      loadNewCollection()     in mainlogic.o
  "user_interface::findFile()", referenced from:
      loadNewCollection()     in mainlogic.o
  "user_interface::displayMainMenu(std::vector<vocabCollection, std::allocator<vocabCollection> >)", referenced from:
      mainlogic()    in mainlogic.o
  "user_interface::getUserAction()", referenced from:
      mainlogic()    in mainlogic.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status
make: *** [cheapassVocab.app/Contents/MacOS/cheapassVocab] Error 1
The process "/usr/bin/make" exited with code 2.
Error while building project cheapassVocab (target: Desktop)
When executing build step 'Make'

What’s happening here?

Answer 1

In the header file, you declare the function findFile in the namespace user_interface. In the cpp file the free function findFile is defined. Yes, you are using namespace user_interface, but the compiler doesn’t know that the findFile defined there belongs to namespace user_interface. The result of all this is that you’ve declared user_interface::findFile and defined ::findFile. When you call user_interface::findFile, the linker cannot find it, since there’s only the free function findFile.

Easily solved – cpp file:

#include "userinterface.h"
using namespace std;

namespace user_interface
{
    string findFile()
    {
        return "./";
    }
}