c++ - 未解析的外部符号 "public: int myclass::get_a (void)"如何解析此代码？菜鸟Q

Question

这里是第一次学习 C++ 的新手程序员。以下是从 Teach Yourself C++ 第三版中摘录的代码。我很想帮助我，我正在学习类，但我无法让这段代码在 visual studio 或 Code::Blocks 上编译。 :(

//#include "stdafx.h"
#include <iostream>
//I understand this. Headers, etc.
using namespace std;
//and this, name traffic management system
class myclass {
    //private to myclass
    int a;
public:
    void set_a(int num);
    int get_a();
};
/*I understand int a is private/inaccessible from the rest of the code
and void set_a(int num) is the dummy function.*/
void myclass::set_a(int num)
//not sure what this is
{
    a = num;
}
/*self explanatory*/
int _tmain(int argc, _TCHAR* argv[])
{
    myclass ob1, ob2;

    ob1.set_a(10);
    ob2.set_a(99);

    cout << ob1.get_a() << "\n";
    cout << ob2.get_a() << "\n";

    return -5;
}
/*This is just supposed to output the number 10 and 99 right?? So why isn't it?*/

在 Visual Studio 上，完整的错误描述是:错误 1 ​​error LNK2019: unresolved external symbol "public: int __thiscall myclass::get_a(void)"(?get_a@myclass@@QAEHXZ) referenced in function _wmain c:\Users\bernardo pliego\documents\visual studio 2013\Projects\Chapter 1.5\Chapter 1.5\Chapter 1.5.obj Chapter 1.5

在 Code::Blocks 上我收到以下错误:在函数“主要”中:对“my_class::get_a()”的 undefined reference

我急需帮助，有人能给我解释一下吗？

Answer 1

因为你没有定义get_a，你只是声明它。添加这样的定义:

int myclass::get_a() { return a; }

或者只是内联定义它:

class myclass {
    //private to myclass
    int a;
public:
    void set_a(int num);
    int get_a() { return a }; 
};