Undefined symbols for typedef and template? [duplicate]

StackOverflow https://stackoverflow.com/questions/9264710

Question

This seems so simple, but I cannot figure out what's wrong. I'm implementing the C++ vector class (only for int, not a template), and functions with iterator templates or typedefs are giving me these errors on compile:

Undefined symbols:
  "void vectorInt::assign<int>(int, int)", referenced from:
      _main in ccNVdR23.o
  "void vectorInt::assign<int*>(int*, int*)", referenced from:
      _main in ccNVdR23.o
      _main in ccNVdR23.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

Important parts for the source files are:

vectorInt.h

#include <cstdlib>
#include <stdexcept>

typedef unsigned int size_type;

class vectorInt {
private:
    int* array;
    size_type current_size;
    size_type current_capacity;
public:
    .
    .
    .
    template <class InputIterator>
        void assign(InputIterator first, InputIterator last);
    void assign(size_type n, const int u);
};

#endif // VECTORINT_H

vectorInt.cpp

#include vectorInt.h
.
.
.
template <class InputIterator>
void vectorInt::assign(InputIterator first, InputIterator last) {
    clear();
    InputIterator it = first;
    int count = 0;
    while(it++ != last) {
        count++;
    }

    reserve(count);
    while(first != last) {
        this->push_back(*first++);
    }
}

void vectorInt::assign(size_type n, const int u) {
    clear();
    reserve(n);

    for(int i=0; i<(int)n; i++)
        push_back(u);
}

main.cpp

#include <cstdlib>
#include <stdexcept>
#include <iostream>
#include "vectorInt.h"

using namespace std;

int main(int argc, char** argv) {
    vectorInt first;
    vectorInt second;
    vectorInt third;

    first.assign(7, 100);

    vectorInt::iterator it;
    it = first.begin()+1;
    second.assign(it, first.end()-1); // the 5 central values of first

    int myints[] = {1776,7,4};
    third.assign(myints, myints+3);   // assigning from array.  

    return 0;
}

FYI: I know the main method uses the vectorInt::iterator, but that is not the problem and hence I didn't include it in the source code.

Was it helpful?

Solution

Template code gets 2 phase compilation. Phase one includes only basic syntax check. The second phase, which is dependent on type T, gets full compilation from compiler. Since your code (implementation) is in CPP file, it would get only first phase compilation, and thus it wont be included in translation unit - No object file would be generated.

For templates, you must allow compiler to compile entire code. And for the same you need to put entire implementation in header file only. You may also #include respective CPP file just after the class declaration.

OTHER TIPS

Place the code for the assign functions in the header file (vectorint.h) and you should be fine. Code for templates needs to be visible when they are instanciated, in you case where you call the assign function.

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