Linking Error 2019

[tepeyton]

I am getting this error message when I compile my code.


Build Output Message:

1>------ Build started: Project: matrixWK06, Configuration: Debug Win32 ------
1>Linking...
1>matrix2Test.obj : error LNK2019: unresolved external symbol "class Matrix __cdecl operator+(class Matrix const &,class Matrix const &)" (??H@YA?AVMatrix@@ABV0@0@Z) referenced in function _main
1>MSVCRTD.lib(crtexew.obj) : error LNK2019: unresolved external symbol _WinMain@16 referenced in function ___tmainCRTStartup
1>C:\ccclibGraphicTest\ccclibGraphicTest\matrixWK06\Debug\matrixWK06.exe : fatal error LNK1120: 2 unresolved externals
1>Build log was saved at "file://c:\ccclibGraphicTest\ccclibGraphicTest\matrixWK06\matrixWK06\Debug\BuildLog.htm"
1>matrixWK06 - 3 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

[imi]

Did you declare some "operator+(Matrix,Matrix)" in some header and forgot to implement it in the C++ file? If so, just implement the operator.

Or the Matrix class isn't your class and you forgot to link to a library which declares the Matrix operator? Then add the library to the linker's "Additional Libraries" in the properties section of the project.

Ciao, Imi

[bluecoder]

try the overloading operator '+' declared as friend function .

[tepeyton]

Here is the code for the header file. Can you tell me what I am missing?

#ifndef MATRIX2_H
#define MATRIX2_H	

#include <iostream>
#include <cassert>

using namespace std;

/**
	This class describes a row in a matrix.
*/
class Matrix;
class MatrixRow
{
public:
	/**
		Remembers a row for a given matrix.
		@param m a pointer to the matrix
		@param s the size of the row
	*/
	MatrixRow(Matrix* m, int s);

	/**
		Accesses a row element.
		@param j the column index
		@return a reference to the element with the given index
	*/
	double& operator[](int j);

private:
	Matrix* mat;
	int i;
};

/**
	This class describes a row in a constant matrix.
*/
class ConstMatrixRow
{
public:
	/**
		Constructs a row with a given start and size.
		@param m a pointer to the matrix
		@param s the size of the row
	*/
	
	ConstMatrixRow(const Matrix* m, int s);

	/**
		Accesses a row element.
		@param j the column index
		@return a reference to the element with the given index
	*/
	double operator[](int j) const;

private:
		const Matrix* mat;
		int i;
};

/**
	This class describes a matrix with arbitrary rows and columns.
*/
class Matrix
{
public:
		/**
			Constructs a matrix filled with zero elements.
		*/
		Matrix(int r, int c);

		/**
			The big three-copy constructor, assignment operator, and destructor.
		*/
		Matrix(const Matrix& other);
		Matrix& operator=(const Matrix& other);
		~Matrix();

		/**
			Gets the number of rows of this matrix.
			@return the number of rows
		*/
		int get_rows() const;

		/**
			Gets the number of columns of this matrix.
			@return the number of columns
		*/
		int get_columns() const;

		/** (NEW - wk06 assignment)
			Negates a matrix.
			@returns the negated matrix.
		*/
		Matrix operator~();

/**
	Accesses a matrix element.
	@param i the row index
	@param j the column index
	@return a reference to the element with the given indexes
*/
double& operator()(int i, int j);

/**
	Accesses a matrix element
	@param i the row index
	@param j the column index
	@return the element with the given indexes
*/
double operator()(int i, int j) const;

/**
	Accesses a matrix row.
	@param i the row index
	@return the row with the given index
*/
MatrixRow operator[](int i);

/**
	Accesses a matrix row.
	@param i the row index
	@return the row with the given index
*/
ConstMatrixRow operator[](int i) const;

/**
	Computes the matrix sum.
	@param right another matrix
	@return the updated matrix
*/
Matrix& operator+=(const Matrix& right);

/** (NEW - wk06 assignment)
	Computes the compound operation of
	matrix subtraction and assignment.
	@param right another matrix
	@return the updated matrix
*/
Matrix operator-=(const Matrix& right);

private:
	/**
		Copies another matrix into this matrix.
		@param other the other matrix
	*/
	void copy(const Matrix& other);

	/**
		Frees the memory for this matrix.
	*/
	void free();

	int rows;
	int columns;
	double* elements;
};

/**(NEW - wk06 assignment)
	Computes the matrix difference (1st implementation).
	@param right another matrix
	@return the difference of two matrices
*/
Matrix operator-(const Matrix& left, const Matrix& right);

/** (NEW - wk06 assignment)
	Computes the matrix difference (2nd implementation).
	@param right another matrix
	@return the difference of two matrices
*/
Matrix operator-(const Matrix& left, Matrix& right);

/**
	Computes the matrix sum.
	@param right another matrix
	@return the sum of two matrices
*/
Matrix operator+(const Matrix& left, const Matrix& right);

/**
	Computes the matrix product.
	@param right another matrix
	@return the product of two matrices
*/
Matrix operator*(const Matrix& left, const Matrix& right);

/** (NEW - wk06 assignment)
	Computes the sum of a scalar value and a matrix.
	@param left a scalar value
	@param right a matrix
	@return the sum of the given value and the given matrix
*/
Matrix operator+(double left, const Matrix& right);

/** (NEW - wk06 assignment)
	Computes the difference of a scalar value and a matrix
	@param left a scalar value
	@param right a matrix
	@return the difference of the given value and the given matrix
*/
Matrix operator-(double left, const Matrix& right);

/**
	Computes the scalar product of a scalar value and a matrix.
	@param left a scalar value
	@param right a matrix
	@return the product of the given value and the given matrix
*/
Matrix operator*(double left, const Matrix& right);

/**
	Computes the sum of a matrix and a scalar value.
	@param right a scalar value
	@return the sum this matrix and the given value
*/
Matrix operator+(const Matrix& left, double right);

/**
	Computes the substraction of a matrix and a scalar value.
	@param right a scalar value
	@return the substraction this matrix and the given value
*/
Matrix operator-(const Matrix& left, double right);

/**
	Computes the scalar product of a matrix and a scalar value.
	@param right a scalar value
	@return the product of this matrix and the given value
*/
Matrix operator*(const Matrix& left, double right);

/**
	Prints a matrix to an output stream.
	@param left an output stream
	@param right a matrix
	@return the given output stream
*/
ostream& operator<<(ostream& left, const Matrix& right);

inline Matrix::Matrix(const Matrix& other)
{
	copy(other);
}

inline Matrix::~Matrix()
{
	free();
}

inline int Matrix::get_rows() const
{
	return rows;
}

inline int Matrix::get_columns() const
{
	return columns;
}

inline void Matrix::free()
{
	delete[] elements;
}

inline double& Matrix::operator()(int i, int j)
{
	assert(0 <= i && i < rows && 0 <= j && j < columns);
	return elements[i * get_columns() + j];
}

inline double Matrix::operator()(int i, int j) const
{
	assert(0 <= i && i < rows && 0 <= j && j < columns);
	return elements[i * get_columns() + j];
}

inline MatrixRow Matrix::operator[](int i)
{
	return MatrixRow(this, i);
}

inline ConstMatrixRow Matrix::operator[](int i) const
{
	return ConstMatrixRow(this, i);
}

inline MatrixRow::MatrixRow(Matrix* m, int s) : mat(m), i(s) { }

inline double& MatrixRow::operator[](int j)
{
	return (*mat)(i,j);
}

inline ConstMatrixRow::ConstMatrixRow(const Matrix* m, int s)
: mat(m), i(s) { }

inline double ConstMatrixRow::operator[](int j) const
{
	return (*mat)(i, j);
}

inline Matrix operator*(double left, const Matrix& right)
{
	return right * left;
}

#endif 

[tepeyton]

Here is the code for the source file. Can you tell me what I am missing?

#include <iomanip>
#include "matrix2.h"

Matrix::Matrix(int r, int c)
	: rows(r), columns(c), elements(new double[rows * columns])
{
	for (int i = 0; i < rows * columns; i++)
		elements[i] = 0;
}

Matrix& Matrix::operator=(const Matrix& other)
{
	if (this != &other)
	{
		free();
		copy(other);
	}
	return *this;
}

void Matrix::copy(const Matrix& other)
{
	rows = other.rows;
	columns = other.columns;
	elements = new double[rows * columns];
	for (int i = 0; i < rows * columns; i++)
		elements[i] = other.elements[i];
}

Matrix& Matrix::operator+=(const Matrix& right)
{
	assert(rows == right.rows && columns == right.columns);
	for (int i = 0; i < rows; i++)
		for (int j = 0; j < columns; j++)
			(*this)(i, j) += right(i, j);
	return *this;
}

Matrix operator+(const Matrix& left, const Matrix& right)
{
	Matrix result = left;
	result += right;
	return result;
}

Matrix operator*(const Matrix& left, const Matrix& right)
{
	assert(left.get_columns() == right.get_rows());
	Matrix result(left.get_rows(), right.get_columns());
	for (int i = 0; i < left.get_rows(); i++)
		for (int j = 0; j < right.get_columns(); j++)
			for (int k = 0; k < left.get_columns(); k++)
				result(i, j) += left(i, k) * right(k, j);
	return result;
}

Matrix operator*(const Matrix& left, double right)
{
	Matrix result(left);
	for (int i = 0; i < result.get_rows(); i++)
		for (int j = 0; j < result.get_columns(); j++)
			result(i, j) *= right;
	return result;
}

ostream& operator<<(ostream& left, const Matrix& right)
{
	const int WIDTH = 10;
	for (int i = 0; i < right.get_rows(); i++)
	{
		for (int j = 0; j < right.get_columns(); j++)
			left << setw(WIDTH) << right(i, j);
		left << "\n";
	}
	return left;
}

[imi]

nope, sorry. Can't tell you. Everything looks fine to me.

Maybe except... did you forget to add the cpp file to your project?

Ciao, Imi.

[tepeyton]

The second code I submitted is the cpp file. I also created a new project thinking that the original was was created as a console file. I ran the new project and still get the 2019 and 1120 link errors.

[tepeyton]

I was able to resolve my problem. I had created the code as a WIN32 Project when I should have created it as a WIN32 Console Application. I tried this and it worked. Thanks to all who had offered their advise.