C++中的接口+实现:代码不执行

我正在阅读Deitel关于C++：如何编程的书。

在一个特定的部分（第3.9节），他们解释了接口和实现的概念。他们还提供了巩固这一概念的示例代码。

尽管我或多或少已经了解了接口和实现分离背后的基本原因，但我无法执行示例代码。示例代码由 3 个文件组成：

1） 成绩簿.h

// GradeBook.h
// GradeBook class definition. This file presents GradeBook's public
// interface without revealing the implementations of GradeBook's member
// functions, which are defined in gradebook.3.12.cpp
#include <string> // class GradeBook uses C++ standard string class
using std::string;
// GradeBook class definition
class GradeBook
{
public:
GradeBook( string ); // constructor that initializes courseName
void setCourseName( string ); // function that sets the course name
string getCourseName(); // function that gets the course name 
void displayMessage(); // function that displays a welcome message
private:
string courseName; // course name for this GradeBook
}; // end class GradeBook

2） 成绩簿.3.12.cpp

// Fig 3.12: GradeBook.cpp
// GradeBook member-function definitions. This file contains
// implementations of the member functions prototyped in GradeBook.h
#include <iostream>
using std::cout;
using std::endl;
#include <string>
using std::string;
#include "GradeBook.h"
// constructor initializes courseName with string supplied as argument
GradeBook::GradeBook( string name )
{
  setCourseName( name );  // call set function to initialize courseName
} // end GradeBook constructor
// function to set the course name
void GradeBook::setCourseName( string name )
{
    courseName = name; // store the course name in the object
} // end function setCourseName
// function to get the course name
string GradeBook::getCourseName()
{
return courseName; // return object's courseName
}// end function getCourseName
// display a welcome message to the GradeBook user
void GradeBook::displayMessage()
{
// call getCourseName to get the courseName
cout << "Welcome to the grade book forn" << getCourseName()
    << "!" << endl;
} // end function displayMessage

3） 成绩簿.3.13.cpp

// GradeBook class demonstration after separating its interface from its implementation
#include <iostream>
using std::cout;
using std::endl;
#include "GradeBook.h" // include definition of class GradeBook
// function main begins program execution
int main()
{
// create two GradeBook objects
GradeBook gradeBook1(" CS101 Intro to C++ programming ");
GradeBook gradeBook2("CS102 Data Structures in C++");
// display initial value of courseName for each GradeBook
cout << "gradeBook1 created for course: " << gradeBook1.getCourseName()
    << "ngradeBook2 created for course: " << gradeBook2.getCourseName()
    << endl;
return 0;
}

要执行和获取类似于 Deitel 书中显示的输出，我必须运行文件 3。o/p 应为"CS101 C++编程入门"，后跟换行符上的"CS101 C++编程入门"。

但是在运行此文件时，我收到以下错误消息 -

Undefined symbols:
"GradeBook::GradeBook(std::basic_string<char, std::char_traits<char>,std::allocator<char> >)", referenced from:
_main in ccaOv3rj.o
_main in ccaOv3rj.o
"GradeBook::getCourseName()", referenced from:
_main in ccaOv3rj.o
_main in ccaOv3rj.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

请解释一下发生了什么。我查找了有关界面和实现的其他帖子 - 发布解决方案的人说必须包含主要功能。但我不认为这是这里的问题。这里还有其他事情我无法弄清楚...可能不是CS专业。

纽伊，非常感谢。