使用Visual Studio2008的C++中的链接错误

Question

其他一切看起来都很好，但最后还是出现了链接错误：

1>Finished searching libraries
1>Finished pass 1
1>Generating non-SAFESEH image.
1>Invoking CVTRES.EXE:
1> /machine:x86
1> /verbose
1> /out:"C:\Users\ocuk\AppData\Local\Temp\lnk9464.tmp"
1> /readonly
1> ".\Debug\Virtual functions.exe.embed.manifest.res"
1>Microsoft (R) Windows Resource To Object Converter Version 9.00.21022.08
1>Copyright (C) Microsoft Corporation.  All rights reserved.
1>adding resource. type:MANIFEST, name:1, language:0x0409, flags:0x30, size:2048
1>fig10_10.obj : error LNK2019: unresolved external symbol "public: virtual void __thiscall Circle::print(void)const " (?print@Circle@@UBEXXZ) referenced in function _main
1>fig10_10.obj : error LNK2019: unresolved external symbol "public: virtual void __thiscall Point::print(void)const " (?print@Point@@UBEXXZ) referenced in function _main
1>C:\Users\ocuk\Documents\C++\Chapter 10\Virtual functions\Debug\Virtual functions.exe : fatal error LNK1120: 2 unresolved externals
1>Build log was saved at "file://c:\Users\ocuk\Documents\C++\Chapter 10\Virtual functions\Virtual functions\Debug\BuildLog.htm"
1>Virtual functions - 3 error(s), 0 warning(s)
========== Rebuild All: 0 succeeded, 1 failed, 0 skipped ==========

在添加VERBOSE之后，我得到一个新的错误：

1>------ Rebuild All started: Project: Virtual functions, Configuration: Debug Win32 ------
1>Deleting intermediate and output files for project 'Virtual functions', configuration 'Debug|Win32'
1>Compiling...
1>circle.cpp
1>fig10_10.cpp
1>point.cpp
1>Generating Code...
1>Compiling manifest to resources...
1>Microsoft (R) Windows (R) Resource Compiler Version 6.0.5724.0
1>Copyright (C) Microsoft Corporation.  All rights reserved.
1>Linking...
1>LINK : fatal error LNK1104: cannot open file 'VERBOSE.obj'
1>Build log was saved at "file://c:\Users\ocuk\Documents\C++\Chapter 10\Virtual    functions\Virtual functions\Debug\BuildLog.htm"
 1>Virtual functions - 1 error(s), 0 warning(s)
========== Rebuild All: 0 succeeded, 1 failed, 0 skipped ==========

当我尝试构建我的项目时，我得到了以下错误。发生的情况是，我已经编写了新的头文件(除了now virtual中的一个函数之外，它们与旧的头文件相同。根据我正在工作的文本，没有必要修改相应的.cpp文件，所以我只是从上一个项目中复制了它们，方法是单击源文件并选择add existing。然后我转到项目属性/“C/C++”/General并添加了.cpp文件所在的路径，但是我仍然得到显示的链接错误：

​

 1>------ Build started: Project: Virtual functions, Configuration: Debug Win32 ------     1>Compiling...     1>circle.cpp     1>point.cpp     1>fig10\_10.cpp     1>Generating Code...     1>Linking...     1>fig10\_10.obj : error LNK2019: unresolved external symbol "public: virtual void       \_\_thiscall Circle::print(void)const " (?print@Circle@@UBEXXZ) referenced in function \_main     1>fig10\_10.obj : error LNK2019: unresolved external symbol "public: virtual void \_\_thiscall Point::print(void)const " (?print@Point@@UBEXXZ) referenced in function \_main     1>C:\Users\ocuk\Documents\C++\Chapter 10\Virtual functions\Debug\Virtual functions.exe   : fatal error LNK1120: 2 unresolved externals     1>Build log was saved at "file://c:\Users\ocuk\Documents\C++\Chapter 10\Virtual functions\Virtual functions\Debug\BuildLog.htm"     1>Virtual functions - 3 error(s), 0 warning(s)     ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

//Fig 10.9:circle.h
 //Circle class contains x-y coordinate pair and radius

#ifndef CIRCLE_H
#define CIRCLE_H

#include "point.h"      //Point class definition

class Circle: public Point{

public:
//default constructor
Circle(int=0, int=0, double=0.0);

void setRadius( double);        //set radius
double getRadius() const;       //return radius

double getDiameter() const;     //return diameter
double getCircumfernce() const; //return circumfernce
double getArea() const;         //return area

virtual void print() const;     //output Circle object

private:
double radius;      //Circle's radius
};

#endif

//Fig. 10.8:point.h
//Point class definition represents an x-y coordinate pair
#ifndef POINT_H
#define POINT_H

class Point{

public:
Point(int=0, int=0);        //default constructor

void setX(int);     //setX in coordinate pair
int getX() const;   //return x in coordinate pair

void setY(int);     //set y in coordinate pair
int getY() const;   //return y from coordinate pair

virtual void print() const;     //output Point object

private:
int x;      //x part of coordinate pair
int y;      //y part of coordinate pair

};


#endif


//Fig 10.4: circle.cpp
// Circle class member-function definitions

#include <iostream>

using std::cout;

#include "circle.h"     //Cicle class definition

//default constructor
Circle::Circle(int xValue, int yValue, double radiusValue):Point (xValue, yValue)//call   base class constructor
{
setRadius(radiusValue);
}//end circle constructor

//set Radius
void Circle::setRadius(double radiusValue)
 {
radius=(radiusValue<0.0?0.0:radiusValue);
}//end fuinction setRadius

//return radius
double Circle::getRadius() const
{
return radius;
}//end finction getRadius

//calculate and return diameter
double Circle::getDiameter() const
{
return 2*getRadius();
}

//calculate and return diameter
double Circle::getCircumference() const
{
return 3.14159*getDiameter();
}

//calculate and return area
double Circle::getArea() const
{
return 3.14159*getRadius()*getRadius();
}//end function getArea

//output Circle object
void Circle::print() const
{
cout << "center = ";
Point::print();     //invoke Point's print function
cout << "; radius = " << getRadius();
}//end function print


//Fig. 10.2:point.cpp
//Point class member function definitions
#include <iostream>

using std::cout;

#include "point.h"      //Point clss deinition

//default constructor
Point::Point(int xValue, int yValue):x(xValue),y(yValue)
{
//empty body
}

//set x in coordinate pair
void Point::setX( int xValue)
{
x=xValue;   //no need for validation
}//end function setX


//return x from coordinate pair
int Point::getX() const
{
return x;
}//end function getX

//set y in coordinate pair
void Point::setY( int yValue)
{
y=yValue;   //no need for validation
}//end function setY


//return y from coordinate pair
int Point::getY() const
{
return y;
}//end function getY

//output Point object
void Point::print() const
{
cout << '[' << getX() << ", " << getY() << ']';

} //end function print


 //Fig. 10.10: fig10_10.cpp
//Introducing polymorphism, virtual functions and dynamic binding

#include <iostream>
using std::cout;
using std::endl;
using std::fixed;

#include <iomanip>

using std::setprecision;

#include "point.h"      //Point class definition
#include "circle.h"     //Circle class definition

int main()
{
Point point(30,50);
Point *pointPtr=0;

Circle circle(120,89,2.7);
Circle *circlePtr=0;

//set floating point precision
cout << fixed <<setprecision(2);

//output objects point and circle using static binding
cout << "Invoking print function on point and circle "
    << "an objects with static binding "
    << "ananPoint: ";
point.print();  //static binding
cout << "anCircle: ";
circle.print(); //static binding

//output pbjects print and cicrle using dynamic binding
cout << "\n\nInvoking print function on point and circle "
    << "\nobjects with dynamic binding";

//aim base-class pointer at base-class object and print
pointPtr=&point;
cout << "\n\nCalling virtual function print with base-class"
    << "\npointer to  a base-class object"
    <<"\ninvokes base-class print function:\n";
pointPtr->print();

//aim derived calss pointer at derived class
//object and print
circlePtr=&circle;
cout << "\n\nCalling virtual function print with "
    <<"\nderived-class pointer to derived class object "
    <<"\ninvokes derived class print function:\n";
circlePtr->print();

//aim-base calss pointer at derive class object and print
pointPtr=&circle;
cout << "\n\nCalling virtual function print with base-class"
    << "\npointer to derived class object "
    <<"\ninvokes derived class print function:\n";
pointPtr->print();      //polymorphiosm invokes ciecle's print
cout << endl;

return 0;

}

Answer 1

井,

Circle::print(void)
Point::print(void)

不会被链接器发现。这意味着要么

• 未生成函数代码
• 您忘记了要链接的.lib文件(请查看项目属性->链接->其他依赖项的输入)

这些都是虚函数，请确保它们是在您的类中的某个位置实现的(如果您想要多态性，则必须在派生类中覆盖它们)。一个纯虚函数可以在最后用“=0”声明，但在这种情况下，你必须在一个派生类中手动实现它。

代码后更新：

你的代码在我看来没问题，只有一个语法错误：

double getCircumfernce() const; //return circumfernce

这阻止了编译。请务必将其更正。

还有:只是为了确认一下..您是否将每段代码放入一个单独的文件中，不是吗？如果您将整个代码放入一个.cpp文件中，您将获得

1>------ Build started: Project: ConsoleApplication2, Configuration: Debug Win32 ------
1>  ConsoleApplication2.cpp
1>ConsoleApplication2.obj : error LNK2005: "public: __thiscall Circle::Circle(int,int,double)" (??0Circle@@QAE@HHN@Z) already defined in circle.obj
1>ConsoleApplication2.obj : error LNK2005: "public: __thiscall Point::Point(int,int)" (??0Point@@QAE@HH@Z) already defined in point.obj

还有很多其他的链接错误..

其他更开放的问题：

• 确保诸如防病毒或防御者之类的东西不会妨碍编译过程(它们可能会阻止MS链接器完成其任务)
• 确保您具有读/写权限(或以administrator)
• Make身份运行VS以确保VS通过如下所述启用/VERBOSE编译标志来找到所有文件(circle.obj、point.obj和fig10_10.obj

Answer 2

我能猜出有两个原因。

1)在旧版本中，你的程序函数print只在基类中定义。现在，您将此函数添加到派生类Point和Circle中。但是您忘记了在cpp模块中定义它们。对于这些类

2)也许您为这些函数添加了限定符const，而旧函数没有限定符const。您又一次忘记了更改cpp模块中函数的定义。