Well i am making a game engine and this is one of its utilities it has. So yes it would be called by other things as regular function.
I changed the code a little:

UtilWindow.h:

Code:
#ifndef __UTILWINDOW_H
#define __UTILWINDOW_H

class UtilWindow
{
public:
	Reshape(int width, int height);
	~Reshape();

private:

};


#endif

UtilWindow.cpp:

Code:
#include <UtilWindow.h>
#include <GL\glew.h>
#include <GL\glut.h>


UtilWindow::Reshape (int width, int height) 
{   
glViewport(0, 0, (GLsizei)width, (GLsizei)height);  
glMatrixMode(GL_PROJECTION);  
glLoadIdentity();   
gluPerspective(60, (GLfloat)width / (GLfloat)height, 1.0, 100.0);   
glMatrixMode(GL_MODELVIEW);  
}

The errors:

Code:
1>------ Build started: Project: Aiedoo, Configuration: Debug Win32 ------
1>  UtilWindow.cpp
1>c:\program files\aiedoo\aiedoo\utility\utilwindow.h(7): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
1>c:\program files\aiedoo\aiedoo\utility\utilwindow.h(7): warning C4183: 'Reshape': missing return type; assumed to be a member function returning 'int'
1>c:\program files\aiedoo\aiedoo\utility\utilwindow.h(8): error C2523: 'UtilWindow::~Reshape' : destructor tag mismatch
1>c:\program files\aiedoo\aiedoo\utility\utilwindow.cpp(7): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int