调用C++类对象与函数时出现Undefined Reference错误求助

问题场景 #

使用Sublime Text编写《C++编程》示例7_15_17的代码，包含fig07_17.cpp、GradeBook.cpp与GradeBook.h三个文件，代码编写完成后编译出现链接错误。

代码文件 #

fig07_17.cpp #

#include <array>
#include "GradeBook.h" 
using namespace std;

// function main begins program execution
int main()
{
   
   const array< int, GradeBook::students > grades = 
      { 87, 68, 94, 100, 83, 78, 85, 91, 76, 87 }; 
   string courseName = "CS101 Introduction to C++ Programming";

   GradeBook myGradeBook( courseName, grades );
   myGradeBook.displayMessage();
   myGradeBook.processGrades(); 
} 

GradeBook.cpp #

// Fig. 7.16: GradeBook.cpp

#include <iostream>
#include <iomanip>
#include "GradeBook.h" 
using namespace std;

GradeBook::GradeBook( const string &name, 
   const array< int, students > &gradesArray )
   : courseName( name ), grades( gradesArray )
{
} 

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

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

void GradeBook::displayMessage() const
{
   cout<< "Welcome to the grade book for\n" << getCourseName() << "!" 
      << endl;
} 

void GradeBook::processGrades() const
{
   // output grades array
   outputGrades();

   // call function getAverage to calculate the average grade
   cout << setprecision( 2 ) << fixed; 
   cout << "\nClass average is " << getAverage() << endl;

   // call functions getMinimum and getMaximum
   cout << "Lowest grade is " << getMinimum() << "\nHighest grade is "
      << getMaximum() << endl;

   // call function outputBarChart to print grade distribution chart
   outputBarChart();
} // end function processGrades

int GradeBook::getMinimum() const
{
   int lowGrade = 100; // assume lowest grade is 100

   // loop through grades array
   for ( int grade : grades )
   {
      // if current grade lower than lowGrade, assign it to lowGrade
      if ( grade < lowGrade )
         lowGrade = grade; // new lowest grade
   } // end for

   return lowGrade; // return lowest grade
} // end function getMinimum

int GradeBook::getMaximum() const
{
   int highGrade = 0; // assume highest grade is 0

   // loop through grades array
   for ( int grade : grades )
   {
      // if current grade higher than highGrade, assign it to highGrade
      if ( grade > highGrade )
         highGrade = grade; // new highest grade
   } // end for

   return highGrade; // return highest grade
} // end function getMaximum     

// determine average grade for test
double GradeBook::getAverage() const
{
   int total = 0; // initialize total

   // sum grades in array
   for ( int grade : grades )
      total += grade;

   // return average of grades
   return static_cast< double >( total ) / grades.size();
} // end function getAverage

void GradeBook::outputBarChart() const
{
   cout << "\nGrade distribution:" << endl;

   // stores frequency of grades in each range of 10 grades
   const size_t frequencySize = 11;
   array< unsigned int, frequencySize > frequency = {}; // init to 0s

   // for each grade, increment the appropriate frequency
   for ( int grade : grades )
      ++frequency[ grade / 10 ];

   
   for ( size_t count = 0; count < frequencySize; ++count ) 
   {
      // output bar labels ("0-9:", ..., "90-99:", "100:" )
      if ( 0 == count )
         cout << "  0-9: ";
      else if ( 10 == count )
         cout << "  100: ";
      else
         cout << count * 10 << "-" << ( count * 10 ) + 9 << ": ";
      
      // print bar of asterisks
      for ( unsigned int stars = 0; stars < frequency[ count ]; ++stars )
         cout << '*';

      cout << endl; // start a new line of output
   } 
} 

void GradeBook::outputGrades() const
{
   cout << "\nThe grades are:\n\n";

   // output each student's grade
   for ( size_t student = 0; student < grades.size(); ++student )
      cout << "Student " << setw( 2 ) << student + 1 << ": " << setw( 3 )
         << grades[ student ] << endl;
} 

GradeBook.h #

#include <string> 
#include <array>

class GradeBook
{
public:
   // constant -- number of students who took the test
   static const size_t students = 10; // note public data

   // constructor initializes course name and array of grades
   GradeBook( const std::string &, const std::array< int, students > & );

   void setCourseName( const std::string & ); 
   std::string getCourseName() const; 
   void displayMessage() const;
   void processGrades() const; 
   int getMinimum() const;  
   int getMaximum() const; 
   double getAverage() const; 
   void outputBarChart() const;
   void outputGrades() const; 
private:
   std::string courseName; 
   std::array< int, students > grades; 
}; 

错误信息 #

C:\Users\PC\AppData\Local\Temp\cciKxoUd.o:fig07_17.cpp:(.text+0xa5): undefined reference to `GradeBook::GradeBook(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::array<int, 10u> const&)'
C:\Users\PC\AppData\Local\Temp\cciKxoUd.o:fig07_17.cpp:(.text+0xb5): undefined reference to `GradeBook::displayMessage() const'
C:\Users\PC\AppData\Local\Temp\cciKxoUd.o:fig07_17.cpp:(.text+0xc2): undefined reference to `GradeBook::processGrades() const'
collect2.exe: error: ld returned 1 exit status
[Finished in 330ms]

解决方法 #

这个错误是链接器错误，核心原因是编译时仅处理了主文件fig07_17.cpp，没有将实现类成员函数的GradeBook.cpp一起编译链接，导致链接器找不到这些函数的具体定义。

方法1：命令行手动编译 #

打开命令提示符，进入代码所在目录，执行以下命令完成编译链接：

g++ fig07_17.cpp GradeBook.cpp -o GradeBook

编译完成后运行可执行文件：

# Windows系统
GradeBook.exe
# Linux/MacOS系统
./GradeBook

方法2：配置Sublime Text编译系统 #

1. 点击Sublime Text菜单栏 Tools -> Build System -> New Build System...
2. 删除默认内容，粘贴以下配置：

{
    "cmd": ["g++", "${file}", "GradeBook.cpp", "-o", "${file_base_name}"],
    "file_regex": "^(..[^:]*):([0-9]+):?([0-9]+)?:? (.*)$",
    "working_dir": "${file_path}",
    "selector": "source.c++",
    "shell": true,
    "variants": [
        {
            "name": "Run",
            "cmd": ["start", "${file_base_name}.exe"]
        }
    ]
}

3. 保存文件，命名为 C++ GradeBook.sublime-build
4. 点击菜单栏 Tools -> Build System，选择刚刚创建的C++ GradeBook，按Ctrl+B编译，按Ctrl+Shift+B运行程序。

额外注意事项 #

检查GradeBook.cpp的文件名是否和代码引用一致，避免因大小写差异（如误写为Gradebook.cpp）导致编译器无法找到文件。

内容的提问来源于stack exchange，提问作者faik mermer