Having trouble compiling multi source-code programs

[Michael369]

In the C++ textbook I'm working through at the moment I'm up to an example where a class is being split into two files. One file, the classes "interface" (member function prototypes and data members) and the other is the implementation of these member functions. The third file in this program is the main function that uses objects of this class.

I'm using Visual studio 2010 to compile my programs, and instead of creating whole new projects for these programs, I am creating the source-code and header files and compiling them using Visual Studios command prompt using the "cl" command.

In this particular example, the class being split into two files is called "GradeBook", and as the name suggest, objects of this class represent a grade book.

Here's the header file for class GradeBook, containing member function prototypes and its data member.

#include <string>

using namespace std;

class GradeBook
{
public:
	GradeBook( string );
	void setCourseName( string );
	string getCourseName();
	void displayMessage();

private:
	string courseName;
};

This next files is the source-code file containing the implementation of GradeBooks member functions

#include <iostream>
#include "GradeBook.h"

using namespace std;

GradeBook::GradeBook( string name )
{
	setCourseName( name );
}

void GradeBook::setCourseName( string name )
{
	courseName = name;
}

string GradeBook::getCourseName()
{
	return courseName;
}

void GradeBook::displayMessage()
{
	cout << "Welcome to the Grade Book for\n" 
		 << getCourseName() << endl;
}

And finally, the file that contains the main function that creates GradeBook objects

#include <iostream>
#include <conio.h>
#include "GradeBook.h"

using namespace std;

int main()
{
	GradeBook myGradeBook1( "CS101 Introduction to C++ programming" );
	GradeBook myGradeBook2( "CS102 Data structures in C++" );

	cout << "The first grade book is for " << myGradeBook1.getCourseName() << endl
		 << "The second grade book is for " << myGradeBook2.getCourseName() << endl;

	getch();
}

All these files are in the same directory, and when I go to compile the Main.cpp file (the one contain main) I get a linker error. I've also tried downloading this source code from the books website to see if that compiled and I got the exact same error, so I know there's nothing wrong with the code, so there must be something wrong with the way I'm compiling it.

[firedraco]

What is the exact command you are putting in to try to compile it?

[4Gb4jE8b]

also does the linker error tell you anything else? And are they of global or unknown scope? it would have to be global (i believe) for it to work correctly

[Computergeek01]

firedraco is on the right track, you're probably right to assume that it's an error in your linker\compiler command line this is why most of us use IDE's after all :D!

But headlessgargoyle is right, you should include as much information as you can in your next post and in the off chance that firedracos idea doesn't lead anywhere the error will tell us what the problem is.

[lionishy]

I've read your code pretending myself to be compiler and throw an error: undefined method link.
According to your main-file (the one you are sending to your compiler) preprocessor is to include the GradeBook.h with prototypes and sending the prepared file to the compiler itself. Compiler sees only prototypes not implementations, cause` he was told to compile your main file, which do not contain any implementation. But it's all right with the compiler, he is leaving an unlinked method to the linker assuming the linker may find the implementation somewhere else.
Then linker look up your methods and shocked! "Where am I supposed to find getCourseName() implementation?!" As you've send only one file it knows nothing about your third file -- implementation.

Thus, you have to compile and assemble (not to link!) your main file and compile (not link!) your implementation file. Then call to linker to link this files.

I hope your book, the one apparently teaching you how to compile multi-source application, helps you to accomplish this task with MS C++ compiler. You, also, might find the proper keys for your 'cl' compiler with -help command, I believe.