Question

I have no idea why this is happening. The error I get is the following:

Error   2   error LNK2019: unresolved external symbol "public: int __thiscall Graphics::GLMatrix::getColumnSize(void)" (?getColumnSize@GLMatrix@Graphics@@QAEHXZ) referenced in function _SDL_main  C:\Users\holland\Documents\code\c++\projects\OpenGL_01\OpenGL_01\main.obj
Error   3   error LNK2019: unresolved external symbol "public: int __thiscall Graphics::GLMatrix::getRowSize(void)" (?getRowSize@GLMatrix@Graphics@@QAEHXZ) referenced in function _SDL_main    C:\Users\holland\Documents\code\c++\projects\OpenGL_01\OpenGL_01\main.obj
Error   4   error LNK1120: 2 unresolved externals   C:\Users\holland\Documents\code\c++\projects\OpenGL_01\Debug\OpenGL_01.exe  

What isn’t being linked is a getRowSize() and getColumnSize() function from my Matrix class. What am I doing wrong?

So, what am I doing wrong here? I’ve been searching…searching every which way.

The Code

Header file:

#ifndef GLMATRIX_H
#define GLMATRIX_H

#pragma once

#include <array>


namespace Graphics {

    class GLMatrix
    {
    public:
        GLMatrix(int sizeX, int sizeY);
        ~GLMatrix();
        void allocMatrix();
        void addColumnI(int row, int column, long item);
        void revertRowsByColumns(); /*changes the formula of r * c to c * r*/
        GLMatrix &operator *(float scalar); /*multiply by scalar*/
        inline int getRowSize();
        inline int getColumnSize();
    private:
        int _sizeX, _sizeY;
        long** _pArray;
    };

}

#endif //GLMATRIX_H

Source:

#include "GLMatrix.h"

namespace Graphics {

    GLMatrix::GLMatrix(int sizeX, int sizeY)
    {
        _sizeX = sizeX; 
        _sizeY = sizeY;
    }

    GLMatrix::~GLMatrix()
    {
        delete _pArray;
    }

    void GLMatrix::addColumnI(int row, int column, long item) {

    }

    inline int GLMatrix::getRowSize() {
        return _sizeX;
    }

    inline int GLMatrix::getColumnSize() {
        return _sizeY;
    }

    void GLMatrix::allocMatrix() {

        _pArray = new long*[_sizeX];

        for (int i = 0; i < _sizeX; ++i) {          
            _pArray[i] = new long[_sizeY];
        }

    }

    void GLMatrix::revertRowsByColumns() {

        long** columns = new long*[_sizeY];

        for (int col = 0; col < _sizeY; ++col) {
            columns[col] = new long[_sizeX];
            memmove(
                columns + col, 
                _pArray[_sizeX - col], 
                sizeof(_sizeX) - sizeof(col)
            );
        }   
    }

}

Main:

#include <SDL.h>
#include "GLMatrix.h"


int main(int argc, char* argv[]) {

    //SDL_Init(SDL_INIT_EVERYTHING);

    //matrix test

    Graphics::GLMatrix* matrix = new Graphics::GLMatrix(3, 3);

    int num_rows = matrix->getRowSize();
    int num_columns = matrix->getColumnSize();
    for (int row = 0; row < num_rows; ++row) {

    }

    //SDL_Quit();

    delete matrix;

    return 0;
}

Answer 1

The common knowledge that inline function MUST be declared in the header file is no longer true. Since several years, most compilers implement a feature called Link Time Optimization (gcc) or Link Time Code Generation (VC) that save important information about inline functions (among others) allowing the linker to look at all the object files as “one big happy translation unit”. Thus the linker can inline functions you put in a cpp file.

Relevant links:
http://msdn.microsoft.com/en-us/library/xbf3tbeh.aspx
http://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html (search for -flto)

Edit: It was apparently not understood from what I wrote earlier. This feature was not designed to save lazy programmers from declaring inline functions in each translation unit. But it does give you this byproduct that can cause problems.
Do declare inline functions in the header file.