Question

我尝试了两种创建类的方法。

1）在与main.cpp相同的文件中创建类，并在与main相同的文件中定义类的成员函数。

2）在单独的（.h）文件中创建类，并在单独的（.cpp）源文件中定义类的成员函数。当我做1）一切都按预期工作。当我这样做2）我不能使用该类而不将初始值传递给构造函数，（默认构造函数）参数似乎不初始化代码或其他东西。我真的很困惑，为什么它在2）中不起作用，但它适用于1）它们应该做同样的事情。

1）main.cpp

#include <iostream>
using namespace std;

class Dog {
public:
    Dog();
    ~Dog();
    int years_old;
};
Dog::Dog() {
    years_old = 10;
    std::cout << "we are inside dog constructor" << std::endl;
}
Dog::~Dog() {}

int main() {
    Dog dogg;
    cout << "Dog is: " << dogg.years_old << "years old!" << endl;
    cout << "We are in main" << endl;
    return 0;
}

2） Dog.h：

#ifndef DOG_H
#define DOG_H
class Dog {
public:
    Dog(); // if I pass in arguments both here and in main and in Dog.cpp this works
    ~Dog();
    int years_old;
};
#endif

2）Dog.cpp

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

Dog::Dog() {
    years_old = 10;
    std::cout << "we are inside dog constructor" << std::endl;
};
Dog::~Dog() {
};

2）main.cpp

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

int main() {
    Dog dogg;
    cout << "Dog is: " << dogg.years_old << "years old!" << endl;
    cout << "We are in main" << endl;
    return 0;
}

我收到此错误：

Undefined symbols for architecture x86_64:
  "Dog::Dog()", referenced from:
      _main in main-ddbb4d.o
  "Dog::~Dog()", referenced from:
      _main in main-ddbb4d.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

没有构造函数参数的类在标题和源分离时无法编译

0 个答案: