an error "symbol(s) not found for architecture x86_64 & linker command failed with exit code 1 "

Question

Sorry if it's a duplicate question, but I've been searching for solution since yesterday and I haven't found out yet..

I'm using CLion on mac, and my compiler is from xcode so i think it's clang. Any help would be appreciated!! Do I need to use gcc? or do I need to fix my cmake?

here's an error message.

[ 33%] Linking CXX executable bag
Undefined symbols for architecture x86_64:
  "Bag<int>::add(int)", referenced from:
      _main in main.cpp.o
  "Bag<int>::print()", referenced from:
      _main in main.cpp.o
  "Bag<int>::Bag()", referenced from:
      _main in main.cpp.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[3]: *** [bag] Error 1
make[2]: *** [CMakeFiles/bag.dir/all] Error 2
make[1]: *** [CMakeFiles/bag.dir/rule] Error 2
make: *** [bag] Error 2

Here's main.cpp

#include <iostream>
#include "Bag.h"

int main() {
    Bag<int> temp;
    temp.add(1);
    temp.print();

    cout << endl;

    return 0;
}

Here's Bag.h.

#ifndef BAG_BAG_H
#define BAG_BAG_H

#include <vector>
#include <cstdlib>
#include <iostream>
using namespace std;

static const size_t CAPACITY = 100;

template <class T>
class Bag{
public:
    Bag();

    size_t size() const;
    bool empty();
    bool check(const T& item);

    void resize(size_t new_size);
    void clear();
    void remove(const T& item);
    void add(T item);
    void print();

private:
    T* data;
    size_t _size;
};


#endif //BAG_BAG_H

Here's Bag.cpp.

#include "Bag.h"

template <class T>
Bag<T>::Bag() : data{new T[CAPACITY]}, _size{0} {}

template <class T>
size_t Bag<T>::size() const {return _size;}

template <class T>
bool Bag<T>::empty() {

}

template <class T>
bool Bag<T>::check(const T &item) {

}

template <class T>
void Bag<T>::resize(size_t new_size) {
    T* temp = new T[new_size];

    for(int i = 0; i == _size; i++)
        *data++ = *temp++;

    delete [] data;
    this->data = &temp;
}

template <class T>
void Bag<T>::add(T item) {
    data[_size + 1] = item;
    _size++;
}

template <class T>
void Bag<T>::print() {
    for(int i = 0; i == _size; i++)
        cout << data[i] << " ";
}

here's CMakeLists.txt

cmake_minimum_required(VERSION 3.15)
project(bag)

set(CMAKE_CXX_STANDARD 14)

add_executable(bag main.cpp Bag.cpp Bag.h)

score 1 · Answer 1 · answered Mar 06 '20 at 21:16

The issue is not you compiler or make system.

This is how templates work in C++: Template code is compiled only when instantiated.

As a result, you can not separate template functions (or class members) in to a separate cpp file, instead you must keep everything in the header file.

Read the last paragraph here: http://www.cplusplus.com/doc/oldtutorial/templates/

an error "symbol(s) not found for architecture x86_64 & linker command failed with exit code 1 "

1 Answers1