C++ Error in object construction. Unresolved External Symbol

Question

I have three files, a main.cpp file meant for testing my functions, a header file for the class, and the cpp file where my objects and members are declared.

I am trying to construct my object Matrix in the main file and receiving error: Error: LNK2019 unresolved external symbol "public: __thiscall Matrix::Matrix(int,int)" (??0Matrix@@QAE@HH@Z) referenced in function _main Matrix Project.

I can only assume this mean there is something wrong with my constructor. I am using it as follows and neither of them work:

    Matrix* matrix = new Matrix(2, 3);
    Matrix test = Matrix(2, 3);

The constructor is declared in the *.h file as follows:

Matrix(int numRows, int numCols);

And then declared in the *.cpp file as follows:

public:
    Matrix(int numRows, int numCols) {
        rows = numRows;
        cols = numCols;
        arr = new double*[numCols];
        for (int i = 0; i < numRows; ++i) {
            for (int x = 0; x < numCols; ++x) {
                arr[i][x] = 0;
            }
        }
    }

Any help is appreciated. I'm sure I'm missing something silly.

Thank you in advance!

[EDIT]

For the sake of information, I figured I'd say that the variables rows, cols, and arr are all declared above the constructor as private members of the class.

Looks like your *.cpp is not compiled before the link phase. — Chris R., Nov 25 '15 at 20:04

score 2 · Accepted Answer · answered Nov 25 '15 at 20:05

In the .cpp file you should put the definition of the method which has been declared in the header (.h) file. Therefore your .cpp file should look like:

Matrix::Matrix(int numRows, int numCols) { }

What you are doing is replicate the class definition in the .cpp file so that why you get the linking error.

score 0 · Answer 2 · answered Nov 25 '15 at 20:06

Maybe I should have posted my entire code so one of you could tell me that I :

A. Will receive an error for redefining the class in my *.cpp file, and

B. Needed to include my *.h file in the *.cpp file so it knows where to get the class declaration. I'm sorry for wasting your time with this.

C++ Error in object construction. Unresolved External Symbol

2 Answers2