Question

我有这样的课程：

class Product
    {
        public :
            virtual double getPrice();
            virtual void setPrice(double price);
    };

class MusicProduct
    {
        protected:

            string author;
            double price;

        public :

            virtual string getAuthor();
            virtual void setAuthor(string author);
            ~MusicProduct();
    };

class CD : public MusicProduct, public Product
    {
        public :

            string getAuthor();
            void setAuthor(string author);
            double getPrice();
            void setPrice(double price);
    };

string CD::getAuthor()
    {
        return MusicProduct::author;
    }

    void CD::setAuthor(string author)
    {
        MusicProduct:author = author;
    }

    void setPrice(double price)
    {
    MusicProduct::price = price;
    }

    double getPrice()
    {
        return MusicProduct::price;
    }

我有这些错误：

/home/katie/Desktop/Temp/MusicStore.cpp||In member function ‘virtual bool  MusicStore::hasProduct( Product)’:|
/home/katie/Desktop/Temp/MusicStore.cpp|15|warning: no return statement in function returning non-void [-Wreturn-type]|
/home/katie/Desktop/Temp/MusicStore.cpp||In member function ‘virtual  Product  MusicStore::getProduct( Product)’:|
/home/katie/Desktop/Temp/MusicStore.cpp|20|warning: no return statement in function returning non-void [-Wreturn-type]|
/home/katie/Desktop/Temp/MusicStore.cpp||In member function ‘virtual bool  MusicStore::buyProduct( Product)’:|
/home/katie/Desktop/Temp/MusicStore.cpp|25|warning: no return statement in function returning non-void [-Wreturn-type]|
/home/katie/Desktop/Temp/MusicStore.cpp||In member function ‘virtual bool  MusicStore::returnProduct( Product)’:|
/home/katie/Desktop/Temp/MusicStore.cpp|30|warning: no return statement in function returning non-void [-Wreturn-type]|
/home/katie/Desktop/Temp/Store/CD.cpp||In member function ‘virtual void  CD::setAuthor(std::string)’:|
/home/katie/Desktop/Temp/Store/CD.cpp|12|warning: label ‘MusicProduct’ defined but not used [-Wunused-label]|
obj/Debug/Store/CD.o:(.rodata._ZTVN5Music2CDE[vtable for  CD]+0x10)||undefined reference to ` CD::getPrice()'|
obj/Debug/Store/CD.o:(.rodata._ZTVN5Music2CDE[vtable for  CD]+0x14)||undefined reference to ` CD::setPrice(double)'|
obj/Debug/Store/CD.o:(.rodata._ZTVN5Music2CDE[vtable for  CD]+0x20)||undefined reference to `non-virtual thunk to  CD::getPrice()'|
obj/Debug/Store/CD.o:(.rodata._ZTVN5Music2CDE[vtable for  CD]+0x24)||undefined reference to `non-virtual thunk to  CD::setPrice(double)'|
obj/Debug/Store/CD.o:(.rodata._ZTIN5Music2CDE[typeinfo for  CD]+0x10)||undefined reference to `typeinfo for  MusicProduct'|
obj/Debug/Store/CD.o:(.rodata._ZTIN5Music2CDE[typeinfo for  CD]+0x18)||undefined reference to `typeinfo for  Product'|
||=== Build finished: 6 errors, 5 warnings ===|

此代码有什么问题？

Answer 1

除了momogentoo提到的缺少CD :: qualifier错误之外，这是另一个非常偷偷摸摸的错误：

void CD::setAuthor(string author)
{
    MusicProduct:author = author; // <-- !!!
}

由于您使用了单个冒号，因此它不会被解释为解析运算符，而是作为标签（对于gotos）。该语句实际上只是为同一个字符串对象进行自我赋值（对于std :: string将没有效果）。

Answer 2

第一个问题：

undefined reference to `CD::getPrice()'

您对该功能的定义缺少CD::资格;所以它改为声明并定义一个非成员函数。

double CD::getPrice()
{//    ^^^^ Add this
MusicProduct::price = price;
}

同样适用于CD::setPrice。

第二个问题：

undefined reference to `typeinfo for  MusicProduct'

据推测，MusicProduct应该是一个抽象类，并且您不希望为其虚函数提供定义。在这种情况下，您必须声明它们纯虚拟：

virtual double getPrice() = 0;
//                        ^^^ Add this

如果它不应该是抽象的，那么你需要实现这些功能。

第三个问题：

In member function ‘virtual bool  MusicStore::hasProduct( Product)’:
warning: no return statement in function returning non-void [-Wreturn-type]

据推测，你有一个名为MusicStore::hasProduct的函数，它应该返回一个布尔值，但不会。

Answer 3

void setPrice（double price） - ＆gt; void CD :: setPrice（double price）

getPrice（）

相同

未定义的引用和非虚拟的thunk

3 个答案: